Nouveau - Aug 2022 - [PATCH v4 00/31] drm/kms: Stop registering multiple /sys/class/backlight devs for a single display

Hi All,

As mentioned in my RFC titled "drm/kms: control display brightness through
drm_connector properties":
https://lore.kernel.org/dri-devel/0d188965-d809-81b5-74ce-7d30c49fee2d at
redhat.com/

The first step towards this is to deal with some existing technical debt
in backlight handling on x86/ACPI boards, specifically we need to stop
registering multiple /sys/class/backlight devs for a single display.

This series implements my RFC describing my plan for these cleanups:
https://lore.kernel.org/dri-devel/98519ba0-7f18-201a-ea34-652f50343158 at
redhat.com/

Changes in version 4:
- Minor tweaks to nvidia-wmi-ec-backlight changes
- Add nouveau_acpi_* wrappers around used include/acpi/video.h functions to
  fix unresolved symbol errors on non X86

Changes in version 3:
- ACPI_VIDEO can now be enabled on non X86 too, adjust various Kconfig changes
- Make the delay before doing fallback acpi_video backlight registration
  a module option (patch 9)
- Move the nvidia-wmi-ec-backlight fw API definitions to a shared header
- Add a "acpi_video_get_backlight_type() ==
acpi_backlight_nvidia_wmi_ec"
  check to the nvidia-wmi-ec-backlight driver (patch 19)

Changes in version 2:
- Introduce acpi_video_backlight_use_native() helper
- Finishes the refactoring, addressing all the bits from the "Other
issues"
  section of the refactor RFC

Note the i915 patches (patch 2 and 12 still need a review/ack, and
I've dropped the previouw review of the nouveau patches because of
changes there. Please review.

This series as submitted is based on drm-tip for CI purposes.
I also have an immutable branch based on 6.0-rc1 with these
same patches available here:
https://git.kernel.org/pub/scm/linux/kernel/git/pdx86/platform-drivers-x86.git/log/?h=backlight-detect-refactor-v4
assuming the i915 patches also pass review I hope to send out
a pull-request to all involved subsystems based on this branch soon.

Regards,

Hans


Hans de Goede (31):
  ACPI: video: Add acpi_video_backlight_use_native() helper
  drm/i915: Don't register backlight when another backlight should be
    used
  drm/amdgpu: Don't register backlight when another backlight should be
    used (v3)
  drm/radeon: Don't register backlight when another backlight should be
    used (v3)
  drm/nouveau: Don't register backlight when another backlight should be
    used (v2)
  ACPI: video: Drop backlight_device_get_by_type() call from
    acpi_video_get_backlight_type()
  ACPI: video: Remove acpi_video_bus from list before tearing it down
  ACPI: video: Simplify acpi_video_unregister_backlight()
  ACPI: video: Make backlight class device registration a separate step
    (v2)
  ACPI: video: Remove code to unregister acpi_video backlight when a
    native backlight registers
  drm/i915: Call acpi_video_register_backlight() (v2)
  drm/nouveau: Register ACPI video backlight when nv_backlight
    registration fails (v2)
  drm/amdgpu: Register ACPI video backlight when skipping amdgpu
    backlight registration
  drm/radeon: Register ACPI video backlight when skipping radeon
    backlight registration
  platform/x86: nvidia-wmi-ec-backlight: Move fw interface definitions
    to a header (v2)
  ACPI: video: Refactor acpi_video_get_backlight_type() a bit
  ACPI: video: Add Nvidia WMI EC brightness control detection (v3)
  ACPI: video: Add Apple GMUX brightness control detection
  platform/x86: nvidia-wmi-ec-backlight: Use
    acpi_video_get_backlight_type()
  platform/x86: apple-gmux: Stop calling acpi/video.h functions
  platform/x86: toshiba_acpi: Stop using
    acpi_video_set_dmi_backlight_type()
  platform/x86: acer-wmi: Move backlight DMI quirks to
    acpi/video_detect.c
  platform/x86: asus-wmi: Drop DMI chassis-type check from backlight
    handling
  platform/x86: asus-wmi: Move acpi_backlight=vendor quirks to ACPI
    video_detect.c
  platform/x86: asus-wmi: Move acpi_backlight=native quirks to ACPI
    video_detect.c
  platform/x86: samsung-laptop: Move acpi_backlight=[vendor|native]
    quirks to ACPI video_detect.c
  ACPI: video: Remove acpi_video_set_dmi_backlight_type()
  ACPI: video: Drop "Samsung X360" acpi_backlight=native quirk
  ACPI: video: Drop NL5x?U, PF4NU1F and PF5?U?? acpi_backlight=native
    quirks
  ACPI: video: Fix indentation of video_detect_dmi_table[] entries
  drm/todo: Add entry about dealing with brightness control on devices
    with > 1 panel

 Documentation/gpu/todo.rst                    |  68 +++
 MAINTAINERS                                   |   1 +
 drivers/acpi/Kconfig                          |   1 +
 drivers/acpi/acpi_video.c                     |  64 ++-
 drivers/acpi/video_detect.c                   | 428 +++++++++++-------
 drivers/gpu/drm/Kconfig                       |  14 +
 .../gpu/drm/amd/amdgpu/atombios_encoders.c    |  14 +-
 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c |   9 +
 drivers/gpu/drm/gma500/Kconfig                |   2 +
 drivers/gpu/drm/i915/Kconfig                  |   2 +
 .../gpu/drm/i915/display/intel_backlight.c    |   7 +
 drivers/gpu/drm/i915/display/intel_display.c  |   8 +
 drivers/gpu/drm/i915/display/intel_panel.c    |   3 +
 drivers/gpu/drm/i915/i915_drv.h               |   2 +
 drivers/gpu/drm/nouveau/nouveau_acpi.c        |  10 +
 drivers/gpu/drm/nouveau/nouveau_acpi.h        |   4 +
 drivers/gpu/drm/nouveau/nouveau_backlight.c   |  13 +
 drivers/gpu/drm/radeon/atombios_encoders.c    |   7 +
 drivers/gpu/drm/radeon/radeon_encoders.c      |  11 +-
 .../gpu/drm/radeon/radeon_legacy_encoders.c   |   7 +
 drivers/platform/x86/Kconfig                  |   1 +
 drivers/platform/x86/acer-wmi.c               |  66 ---
 drivers/platform/x86/apple-gmux.c             |   3 -
 drivers/platform/x86/asus-nb-wmi.c            |  21 -
 drivers/platform/x86/asus-wmi.c               |  13 -
 drivers/platform/x86/asus-wmi.h               |   2 -
 drivers/platform/x86/eeepc-wmi.c              |  25 +-
 .../platform/x86/nvidia-wmi-ec-backlight.c    |  82 +---
 drivers/platform/x86/samsung-laptop.c         |  87 ----
 drivers/platform/x86/toshiba_acpi.c           |  16 -
 include/acpi/video.h                          |   9 +-
 .../x86/nvidia-wmi-ec-backlight.h             |  76 ++++
 32 files changed, 570 insertions(+), 506 deletions(-)
 create mode 100644 include/linux/platform_data/x86/nvidia-wmi-ec-backlight.h

-- 
2.37.2

ATM on x86 laptops where we want userspace to use the acpi_video backlight
device we often register both the GPU's native backlight device and
acpi_video's firmware acpi_video# backlight device. This relies on
userspace preferring firmware type backlight devices over native ones, but
registering 2 backlight devices for a single display really is undesirable.

On x86 laptops where the native GPU backlight device should be used,
the registering of other backlight devices is avoided by their drivers
using acpi_video_get_backlight_type() and only registering their backlight
if the return value matches their type.

acpi_video_get_backlight_type() uses
backlight_device_get_by_type(BACKLIGHT_RAW) to determine if a native
driver is available and will never return native if this returns
false. This means that the GPU's native backlight registering code
cannot just call acpi_video_get_backlight_type() to determine if it
should register its backlight, since acpi_video_get_backlight_type() will
never return native until the native backlight has already registered.

To fix this add a new internal native function parameter to
acpi_video_get_backlight_type(), which when set to true will make
acpi_video_get_backlight_type() behave as if a native backlight has
already been registered.

And add a new acpi_video_backlight_use_native() helper, which sets this
to true, for use in native GPU backlight code.

Changes in v2:
- Replace adding a native parameter to acpi_video_get_backlight_type() with
  adding a new acpi_video_backlight_use_native() helper.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/video_detect.c | 24 ++++++++++++++++++++----
 include/acpi/video.h        |  5 +++++
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index 5d7f38016a24..5f105eaa7d30 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -17,8 +17,9 @@
  * Otherwise vendor specific drivers like thinkpad_acpi, asus-laptop,
  * sony_acpi,... can take care about backlight brightness.
  *
- * Backlight drivers can use acpi_video_get_backlight_type() to determine
- * which driver should handle the backlight.
+ * Backlight drivers can use acpi_video_get_backlight_type() to determine which
+ * driver should handle the backlight. RAW/GPU-driver backlight drivers must
+ * use the acpi_video_backlight_use_native() helper for this.
  *
  * If CONFIG_ACPI_VIDEO is neither set as "compiled in" (y) nor as a
module (m)
  * this file will not be compiled and acpi_video_get_backlight_type() will
@@ -571,9 +572,10 @@ static int acpi_video_backlight_notify(struct
notifier_block *nb,
  * Arguably the native on win8 check should be done first, but that would
  * be a behavior change, which may causes issues.
  */
-enum acpi_backlight_type acpi_video_get_backlight_type(void)
+static enum acpi_backlight_type __acpi_video_get_backlight_type(bool native)
 {
 	static DEFINE_MUTEX(init_mutex);
+	static bool native_available;
 	static bool init_done;
 	static long video_caps;
 
@@ -593,6 +595,8 @@ enum acpi_backlight_type acpi_video_get_backlight_type(void)
 			backlight_notifier_registered = true;
 		init_done = true;
 	}
+	if (native)
+		native_available = true;
 	mutex_unlock(&init_mutex);
 
 	if (acpi_backlight_cmdline != acpi_backlight_undef)
@@ -604,13 +608,25 @@ enum acpi_backlight_type
acpi_video_get_backlight_type(void)
 	if (!(video_caps & ACPI_VIDEO_BACKLIGHT))
 		return acpi_backlight_vendor;
 
-	if (acpi_osi_is_win8() && backlight_device_get_by_type(BACKLIGHT_RAW))
+	if (acpi_osi_is_win8() &&
+	    (native_available || backlight_device_get_by_type(BACKLIGHT_RAW)))
 		return acpi_backlight_native;
 
 	return acpi_backlight_video;
 }
+
+enum acpi_backlight_type acpi_video_get_backlight_type(void)
+{
+	return __acpi_video_get_backlight_type(false);
+}
 EXPORT_SYMBOL(acpi_video_get_backlight_type);
 
+bool acpi_video_backlight_use_native(void)
+{
+	return __acpi_video_get_backlight_type(true) == acpi_backlight_native;
+}
+EXPORT_SYMBOL(acpi_video_backlight_use_native);
+
 /*
  * Set the preferred backlight interface type based on DMI info.
  * This function allows DMI blacklists to be implemented by external
diff --git a/include/acpi/video.h b/include/acpi/video.h
index db8548ff03ce..4705e339c252 100644
--- a/include/acpi/video.h
+++ b/include/acpi/video.h
@@ -56,6 +56,7 @@ extern void acpi_video_unregister(void);
 extern int acpi_video_get_edid(struct acpi_device *device, int type,
 			       int device_id, void **edid);
 extern enum acpi_backlight_type acpi_video_get_backlight_type(void);
+extern bool acpi_video_backlight_use_native(void);
 extern void acpi_video_set_dmi_backlight_type(enum acpi_backlight_type type);
 /*
  * Note: The value returned by acpi_video_handles_brightness_key_presses()
@@ -77,6 +78,10 @@ static inline enum acpi_backlight_type
acpi_video_get_backlight_type(void)
 {
 	return acpi_backlight_vendor;
 }
+static inline bool acpi_video_backlight_use_native(void)
+{
+	return true;
+}
 static inline void acpi_video_set_dmi_backlight_type(enum acpi_backlight_type
type)
 {
 }
-- 
2.37.2

Before this commit when we want userspace to use the acpi_video backlight
device we register both the GPU's native backlight device and
acpi_video's
firmware acpi_video# backlight device. This relies on userspace preferring
firmware type backlight devices over native ones.

Registering 2 backlight devices for a single display really is
undesirable, don't register the GPU's native backlight device when
another backlight device should be used.

Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/gpu/drm/i915/display/intel_backlight.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_backlight.c
b/drivers/gpu/drm/i915/display/intel_backlight.c
index 681ebcda97ad..a4dd7924e0c1 100644
--- a/drivers/gpu/drm/i915/display/intel_backlight.c
+++ b/drivers/gpu/drm/i915/display/intel_backlight.c
@@ -8,6 +8,8 @@
 #include <linux/pwm.h>
 #include <linux/string_helpers.h>
 
+#include <acpi/video.h>
+
 #include "intel_backlight.h"
 #include "intel_backlight_regs.h"
 #include "intel_connector.h"
@@ -952,6 +954,11 @@ int intel_backlight_device_register(struct intel_connector
*connector)
 
 	WARN_ON(panel->backlight.max == 0);
 
+	if (!acpi_video_backlight_use_native()) {
+		DRM_INFO("Skipping intel_backlight registration\n");
+		return 0;
+	}
+
 	memset(&props, 0, sizeof(props));
 	props.type = BACKLIGHT_RAW;
 
-- 
2.37.2

Before this commit when we want userspace to use the acpi_video backlight
device we register both the GPU's native backlight device and
acpi_video's
firmware acpi_video# backlight device. This relies on userspace preferring
firmware type backlight devices over native ones.

Registering 2 backlight devices for a single display really is
undesirable, don't register the GPU's native backlight device when
another backlight device should be used.

Changes in v2:
- To avoid linker errors when amdgpu is builtin and video_detect.c is in
  a module, select ACPI_VIDEO and its deps if ACPI is enabled.
  When ACPI is disabled, ACPI_VIDEO is also always disabled, ensuring
  the stubs from acpi/video.h will be used.

Changes in v3:
- Use drm_info(drm_dev, "...") to log messages
- ACPI_VIDEO can now be enabled on non X86 too,
  adjust the Kconfig changes to match this.

Acked-by: Alex Deucher <alexander.deucher at amd.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/gpu/drm/Kconfig                           | 7 +++++++
 drivers/gpu/drm/amd/amdgpu/atombios_encoders.c    | 7 +++++++
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 7 +++++++
 3 files changed, 21 insertions(+)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 0b2ad7212ee6..95ca33938b4a 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -259,6 +259,13 @@ config DRM_AMDGPU
 	select BACKLIGHT_CLASS_DEVICE
 	select INTERVAL_TREE
 	select DRM_BUDDY
+	# amdgpu depends on ACPI_VIDEO when ACPI is enabled, for select to work
+	# ACPI_VIDEO's dependencies must also be selected.
+	select INPUT if ACPI
+	select ACPI_VIDEO if ACPI
+	# On x86 ACPI_VIDEO also needs ACPI_WMI
+	select X86_PLATFORM_DEVICES if ACPI && X86
+	select ACPI_WMI if ACPI && X86
 	help
 	  Choose this option if you have a recent AMD Radeon graphics card.
 
diff --git a/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c
b/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c
index fa7421afb9a6..b4e3cedceaf8 100644
--- a/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c
+++ b/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c
@@ -26,6 +26,8 @@
 
 #include <linux/pci.h>
 
+#include <acpi/video.h>
+
 #include <drm/drm_crtc_helper.h>
 #include <drm/amdgpu_drm.h>
 #include "amdgpu.h"
@@ -184,6 +186,11 @@ void amdgpu_atombios_encoder_init_backlight(struct
amdgpu_encoder *amdgpu_encode
 	if (!(adev->mode_info.firmware_flags &
ATOM_BIOS_INFO_BL_CONTROLLED_BY_GPU))
 		return;
 
+	if (!acpi_video_backlight_use_native()) {
+		drm_info(dev, "Skipping amdgpu atom DIG backlight registration\n");
+		return;
+	}
+
 	pdata = kmalloc(sizeof(struct amdgpu_backlight_privdata), GFP_KERNEL);
 	if (!pdata) {
 		DRM_ERROR("Memory allocation failed\n");
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index e702f0d72d53..706c67f4bda8 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -90,6 +90,8 @@
 #include <drm/drm_gem_atomic_helper.h>
 #include <drm/drm_plane_helper.h>
 
+#include <acpi/video.h>
+
 #include "ivsrcid/dcn/irqsrcs_dcn_1_0.h"
 
 #include "dcn/dcn_1_0_offset.h"
@@ -4033,6 +4035,11 @@ amdgpu_dm_register_backlight_device(struct
amdgpu_display_manager *dm)
 	amdgpu_dm_update_backlight_caps(dm, dm->num_of_edps);
 	dm->brightness[dm->num_of_edps] = AMDGPU_MAX_BL_LEVEL;
 
+	if (!acpi_video_backlight_use_native()) {
+		drm_info(adev_to_drm(dm->adev), "Skipping amdgpu DM backlight
registration\n");
+		return;
+	}
+
 	props.max_brightness = AMDGPU_MAX_BL_LEVEL;
 	props.brightness = AMDGPU_MAX_BL_LEVEL;
 	props.type = BACKLIGHT_RAW;
-- 
2.37.2

Before this commit when we want userspace to use the acpi_video backlight
device we register both the GPU's native backlight device and
acpi_video's
firmware acpi_video# backlight device. This relies on userspace preferring
firmware type backlight devices over native ones.

Registering 2 backlight devices for a single display really is
undesirable, don't register the GPU's native backlight device when
another backlight device should be used.

Changes in v2:
- To avoid linker errors when amdgpu is builtin and video_detect.c is in
  a module, select ACPI_VIDEO and its deps if ACPI is enabled.
  When ACPI is disabled, ACPI_VIDEO is also always disabled, ensuring
  the stubs from acpi/video.h will be used.

Changes in v3:
- Use drm_info(drm_dev, "...") to log messages
- ACPI_VIDEO can now be enabled on non X86 too,
  adjust the Kconfig changes to match this.

Acked-by: Alex Deucher <alexander.deucher at amd.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/gpu/drm/Kconfig                         | 7 +++++++
 drivers/gpu/drm/radeon/atombios_encoders.c      | 7 +++++++
 drivers/gpu/drm/radeon/radeon_legacy_encoders.c | 7 +++++++
 3 files changed, 21 insertions(+)

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 95ca33938b4a..0471505e951d 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -234,6 +234,13 @@ config DRM_RADEON
 	select HWMON
 	select BACKLIGHT_CLASS_DEVICE
 	select INTERVAL_TREE
+	# radeon depends on ACPI_VIDEO when ACPI is enabled, for select to work
+	# ACPI_VIDEO's dependencies must also be selected.
+	select INPUT if ACPI
+	select ACPI_VIDEO if ACPI
+	# On x86 ACPI_VIDEO also needs ACPI_WMI
+	select X86_PLATFORM_DEVICES if ACPI && X86
+	select ACPI_WMI if ACPI && X86
 	help
 	  Choose this option if you have an ATI Radeon graphics card.  There
 	  are both PCI and AGP versions.  You don't need to choose this to
diff --git a/drivers/gpu/drm/radeon/atombios_encoders.c
b/drivers/gpu/drm/radeon/atombios_encoders.c
index 0eae05dfb385..c841c273222e 100644
--- a/drivers/gpu/drm/radeon/atombios_encoders.c
+++ b/drivers/gpu/drm/radeon/atombios_encoders.c
@@ -32,6 +32,8 @@
 #include <drm/drm_file.h>
 #include <drm/radeon_drm.h>
 
+#include <acpi/video.h>
+
 #include "atom.h"
 #include "radeon_atombios.h"
 #include "radeon.h"
@@ -209,6 +211,11 @@ void radeon_atom_backlight_init(struct radeon_encoder
*radeon_encoder,
 	if (!(rdev->mode_info.firmware_flags &
ATOM_BIOS_INFO_BL_CONTROLLED_BY_GPU))
 		return;
 
+	if (!acpi_video_backlight_use_native()) {
+		drm_info(dev, "Skipping radeon atom DIG backlight registration\n");
+		return;
+	}
+
 	pdata = kmalloc(sizeof(struct radeon_backlight_privdata), GFP_KERNEL);
 	if (!pdata) {
 		DRM_ERROR("Memory allocation failed\n");
diff --git a/drivers/gpu/drm/radeon/radeon_legacy_encoders.c
b/drivers/gpu/drm/radeon/radeon_legacy_encoders.c
index 1a66fb969ee7..0cd32c65456c 100644
--- a/drivers/gpu/drm/radeon/radeon_legacy_encoders.c
+++ b/drivers/gpu/drm/radeon/radeon_legacy_encoders.c
@@ -33,6 +33,8 @@
 #include <drm/drm_util.h>
 #include <drm/radeon_drm.h>
 
+#include <acpi/video.h>
+
 #include "radeon.h"
 #include "radeon_asic.h"
 #include "radeon_legacy_encoders.h"
@@ -387,6 +389,11 @@ void radeon_legacy_backlight_init(struct radeon_encoder
*radeon_encoder,
 		return;
 #endif
 
+	if (!acpi_video_backlight_use_native()) {
+		drm_info(dev, "Skipping radeon legacy LVDS backlight
registration\n");
+		return;
+	}
+
 	pdata = kmalloc(sizeof(struct radeon_backlight_privdata), GFP_KERNEL);
 	if (!pdata) {
 		DRM_ERROR("Memory allocation failed\n");
-- 
2.37.2

Before this commit when we want userspace to use the acpi_video backlight
device we register both the GPU's native backlight device and
acpi_video's
firmware acpi_video# backlight device. This relies on userspace preferring
firmware type backlight devices over native ones.

Registering 2 backlight devices for a single display really is
undesirable, don't register the GPU's native backlight device when
another backlight device should be used.

Changes in v2:
- Add nouveau_acpi_video_backlight_use_native() wrapper to avoid unresolved
  symbol errors on non X86

Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/gpu/drm/nouveau/nouveau_acpi.c      | 5 +++++
 drivers/gpu/drm/nouveau/nouveau_acpi.h      | 2 ++
 drivers/gpu/drm/nouveau/nouveau_backlight.c | 6 ++++++
 3 files changed, 13 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/nouveau_acpi.c
b/drivers/gpu/drm/nouveau/nouveau_acpi.c
index 6140db756d06..1592c9cd7750 100644
--- a/drivers/gpu/drm/nouveau/nouveau_acpi.c
+++ b/drivers/gpu/drm/nouveau/nouveau_acpi.c
@@ -386,3 +386,8 @@ nouveau_acpi_edid(struct drm_device *dev, struct
drm_connector *connector)
 
 	return kmemdup(edid, EDID_LENGTH, GFP_KERNEL);
 }
+
+bool nouveau_acpi_video_backlight_use_native(void)
+{
+	return acpi_video_backlight_use_native();
+}
diff --git a/drivers/gpu/drm/nouveau/nouveau_acpi.h
b/drivers/gpu/drm/nouveau/nouveau_acpi.h
index 330f9b837066..3c666c30dfca 100644
--- a/drivers/gpu/drm/nouveau/nouveau_acpi.h
+++ b/drivers/gpu/drm/nouveau/nouveau_acpi.h
@@ -11,6 +11,7 @@ void nouveau_register_dsm_handler(void);
 void nouveau_unregister_dsm_handler(void);
 void nouveau_switcheroo_optimus_dsm(void);
 void *nouveau_acpi_edid(struct drm_device *, struct drm_connector *);
+bool nouveau_acpi_video_backlight_use_native(void);
 #else
 static inline bool nouveau_is_optimus(void) { return false; };
 static inline bool nouveau_is_v1_dsm(void) { return false; };
@@ -18,6 +19,7 @@ static inline void nouveau_register_dsm_handler(void) {}
 static inline void nouveau_unregister_dsm_handler(void) {}
 static inline void nouveau_switcheroo_optimus_dsm(void) {}
 static inline void *nouveau_acpi_edid(struct drm_device *dev, struct
drm_connector *connector) { return NULL; }
+static inline bool nouveau_acpi_video_backlight_use_native(void) { return true;
}
 #endif
 
 #endif
diff --git a/drivers/gpu/drm/nouveau/nouveau_backlight.c
b/drivers/gpu/drm/nouveau/nouveau_backlight.c
index a2141d3d9b1d..d2b8f8c13db4 100644
--- a/drivers/gpu/drm/nouveau/nouveau_backlight.c
+++ b/drivers/gpu/drm/nouveau/nouveau_backlight.c
@@ -38,6 +38,7 @@
 #include "nouveau_reg.h"
 #include "nouveau_encoder.h"
 #include "nouveau_connector.h"
+#include "nouveau_acpi.h"
 
 static struct ida bl_ida;
 #define BL_NAME_SIZE 15 // 12 for name + 2 for digits + 1 for '\0'
@@ -405,6 +406,11 @@ nouveau_backlight_init(struct drm_connector *connector)
 		goto fail_alloc;
 	}
 
+	if (!nouveau_acpi_video_backlight_use_native()) {
+		NV_INFO(drm, "Skipping nv_backlight registration\n");
+		goto fail_alloc;
+	}
+
 	if (!nouveau_get_backlight_name(backlight_name, bl)) {
 		NV_ERROR(drm, "Failed to retrieve a unique name for the backlight
interface\n");
 		goto fail_alloc;
-- 
2.37.2

All x86/ACPI kms drivers which register native/BACKLIGHT_RAW type
backlight devices call acpi_video_backlight_use_native() now. This sets
__acpi_video_get_backlight_type()'s internal static native_available flag.

This makes the backlight_device_get_by_type(BACKLIGHT_RAW) check
unnecessary.

Relying on the cached native_available value not only is simpler, it will
also work correctly in cases where then native backlight registration was
skipped because of acpi_video_backlight_use_native() returning false.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/video_detect.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index 5f105eaa7d30..385eb49c763f 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -608,8 +608,7 @@ static enum acpi_backlight_type
__acpi_video_get_backlight_type(bool native)
 	if (!(video_caps & ACPI_VIDEO_BACKLIGHT))
 		return acpi_backlight_vendor;
 
-	if (acpi_osi_is_win8() &&
-	    (native_available || backlight_device_get_by_type(BACKLIGHT_RAW)))
+	if (acpi_osi_is_win8() && native_available)
 		return acpi_backlight_native;
 
 	return acpi_backlight_video;
-- 
2.37.2

Move the list_del removing an acpi_video_bus from video_bus_head
on teardown to before the teardown is done, to avoid code iterating
over the video_bus_head list seeing acpi_video_bus objects on there
which are (partly) torn down already.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/acpi_video.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
index 5cbe2196176d..cde8ffa9f0b8 100644
--- a/drivers/acpi/acpi_video.c
+++ b/drivers/acpi/acpi_video.c
@@ -2111,14 +2111,14 @@ static int acpi_video_bus_remove(struct acpi_device
*device)
 
 	video = acpi_driver_data(device);
 
-	acpi_video_bus_remove_notify_handler(video);
-	acpi_video_bus_unregister_backlight(video);
-	acpi_video_bus_put_devices(video);
-
 	mutex_lock(&video_list_lock);
 	list_del(&video->entry);
 	mutex_unlock(&video_list_lock);
 
+	acpi_video_bus_remove_notify_handler(video);
+	acpi_video_bus_unregister_backlight(video);
+	acpi_video_bus_put_devices(video);
+
 	kfree(video->attached_array);
 	kfree(video);
 
-- 
2.37.2

When acpi_video_register() has not run yet the video_bus_head will be
empty, so there is no need to check the register_count flag first.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/acpi_video.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
index cde8ffa9f0b8..8545bf94866f 100644
--- a/drivers/acpi/acpi_video.c
+++ b/drivers/acpi/acpi_video.c
@@ -2257,14 +2257,10 @@ void acpi_video_unregister_backlight(void)
 {
 	struct acpi_video_bus *video;
 
-	mutex_lock(&register_count_mutex);
-	if (register_count) {
-		mutex_lock(&video_list_lock);
-		list_for_each_entry(video, &video_bus_head, entry)
-			acpi_video_bus_unregister_backlight(video);
-		mutex_unlock(&video_list_lock);
-	}
-	mutex_unlock(&register_count_mutex);
+	mutex_lock(&video_list_lock);
+	list_for_each_entry(video, &video_bus_head, entry)
+		acpi_video_bus_unregister_backlight(video);
+	mutex_unlock(&video_list_lock);
 }
 
 bool acpi_video_handles_brightness_key_presses(void)
-- 
2.37.2

On x86/ACPI boards the acpi_video driver will usually initialize before
the kms driver (except i915). This causes /sys/class/backlight/acpi_video0
to show up and then the kms driver registers its own native backlight
device after which the drivers/acpi/video_detect.c code unregisters
the acpi_video0 device (when acpi_video_get_backlight_type()==native).

This means that userspace briefly sees 2 devices and the disappearing of
acpi_video0 after a brief time confuses the systemd backlight level
save/restore code, see e.g.:
https://bbs.archlinux.org/viewtopic.php?id=269920

To fix this make backlight class device registration a separate step
done by a new acpi_video_register_backlight() function. The intend is for
this to be called by the drm/kms driver *after* it is done setting up its
own native backlight device. So that acpi_video_get_backlight_type() knows
if a native backlight will be available or not at acpi_video backlight
registration time, avoiding the add + remove dance.

Note the new acpi_video_register_backlight() function is also called from
a delayed work to ensure that the acpi_video backlight devices does get
registered if necessary even if there is no drm/kms driver or when it is
disabled.

Changes in v2:
- Make register_backlight_delay a module parameter, mainly so that it can
  be disabled by Nvidia binary driver users

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/acpi_video.c | 50 ++++++++++++++++++++++++++++++++++++---
 include/acpi/video.h      |  2 ++
 2 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
index 8545bf94866f..09dd86f86cf3 100644
--- a/drivers/acpi/acpi_video.c
+++ b/drivers/acpi/acpi_video.c
@@ -73,6 +73,16 @@ module_param(device_id_scheme, bool, 0444);
 static int only_lcd = -1;
 module_param(only_lcd, int, 0444);
 
+/*
+ * Display probing is known to take up to 5 seconds, so delay the fallback
+ * backlight registration by 5 seconds + 3 seconds for some extra margin.
+ */
+static int register_backlight_delay = 8;
+module_param(register_backlight_delay, int, 0444);
+MODULE_PARM_DESC(register_backlight_delay,
+	"Delay in seconds before doing fallback (non GPU driver triggered) "
+	"backlight registration, set to 0 to disable.");
+
 static bool may_report_brightness_keys;
 static int register_count;
 static DEFINE_MUTEX(register_count_mutex);
@@ -81,6 +91,9 @@ static LIST_HEAD(video_bus_head);
 static int acpi_video_bus_add(struct acpi_device *device);
 static int acpi_video_bus_remove(struct acpi_device *device);
 static void acpi_video_bus_notify(struct acpi_device *device, u32 event);
+static void acpi_video_bus_register_backlight_work(struct work_struct
*ignored);
+static DECLARE_DELAYED_WORK(video_bus_register_backlight_work,
+			    acpi_video_bus_register_backlight_work);
 void acpi_video_detect_exit(void);
 
 /*
@@ -1859,8 +1872,6 @@ static int acpi_video_bus_register_backlight(struct
acpi_video_bus *video)
 	if (video->backlight_registered)
 		return 0;
 
-	acpi_video_run_bcl_for_osi(video);
-
 	if (acpi_video_get_backlight_type() != acpi_backlight_video)
 		return 0;
 
@@ -2086,7 +2097,11 @@ static int acpi_video_bus_add(struct acpi_device *device)
 	list_add_tail(&video->entry, &video_bus_head);
 	mutex_unlock(&video_list_lock);
 
-	acpi_video_bus_register_backlight(video);
+	/*
+	 * The userspace visible backlight_device gets registered separately
+	 * from acpi_video_register_backlight().
+	 */
+	acpi_video_run_bcl_for_osi(video);
 	acpi_video_bus_add_notify_handler(video);
 
 	return 0;
@@ -2125,6 +2140,11 @@ static int acpi_video_bus_remove(struct acpi_device
*device)
 	return 0;
 }
 
+static void acpi_video_bus_register_backlight_work(struct work_struct *ignored)
+{
+	acpi_video_register_backlight();
+}
+
 static int __init is_i740(struct pci_dev *dev)
 {
 	if (dev->device == 0x00D1)
@@ -2235,6 +2255,18 @@ int acpi_video_register(void)
 	 */
 	register_count = 1;
 
+	/*
+	 * acpi_video_bus_add() skips registering the userspace visible
+	 * backlight_device. The intend is for this to be registered by the
+	 * drm/kms driver calling acpi_video_register_backlight() *after* it is
+	 * done setting up its own native backlight device. The delayed work
+	 * ensures that acpi_video_register_backlight() always gets called
+	 * eventually, in case there is no drm/kms driver or it is disabled.
+	 */
+	if (register_backlight_delay)
+		schedule_delayed_work(&video_bus_register_backlight_work,
+				      register_backlight_delay * HZ);
+
 leave:
 	mutex_unlock(&register_count_mutex);
 	return ret;
@@ -2245,6 +2277,7 @@ void acpi_video_unregister(void)
 {
 	mutex_lock(&register_count_mutex);
 	if (register_count) {
+		cancel_delayed_work_sync(&video_bus_register_backlight_work);
 		acpi_bus_unregister_driver(&acpi_video_bus);
 		register_count = 0;
 		may_report_brightness_keys = false;
@@ -2253,6 +2286,17 @@ void acpi_video_unregister(void)
 }
 EXPORT_SYMBOL(acpi_video_unregister);
 
+void acpi_video_register_backlight(void)
+{
+	struct acpi_video_bus *video;
+
+	mutex_lock(&video_list_lock);
+	list_for_each_entry(video, &video_bus_head, entry)
+		acpi_video_bus_register_backlight(video);
+	mutex_unlock(&video_list_lock);
+}
+EXPORT_SYMBOL(acpi_video_register_backlight);
+
 void acpi_video_unregister_backlight(void)
 {
 	struct acpi_video_bus *video;
diff --git a/include/acpi/video.h b/include/acpi/video.h
index 4705e339c252..0625806d3bbd 100644
--- a/include/acpi/video.h
+++ b/include/acpi/video.h
@@ -53,6 +53,7 @@ enum acpi_backlight_type {
 #if IS_ENABLED(CONFIG_ACPI_VIDEO)
 extern int acpi_video_register(void);
 extern void acpi_video_unregister(void);
+extern void acpi_video_register_backlight(void);
 extern int acpi_video_get_edid(struct acpi_device *device, int type,
 			       int device_id, void **edid);
 extern enum acpi_backlight_type acpi_video_get_backlight_type(void);
@@ -69,6 +70,7 @@ extern int acpi_video_get_levels(struct acpi_device *device,
 #else
 static inline int acpi_video_register(void) { return -ENODEV; }
 static inline void acpi_video_unregister(void) { return; }
+static inline void acpi_video_register_backlight(void) { return; }
 static inline int acpi_video_get_edid(struct acpi_device *device, int type,
 				      int device_id, void **edid)
 {
-- 
2.37.2

Remove the code to unregister acpi_video backlight devices when
a native backlight device gets registered later.

Now that the acpi_video backlight device registration is a separate step
which runs later, after the drm/kms driver is done setting up its own
native backlight device, it is no longer necessary to monitor for a
native (BACKLIGHT_RAW) device showing up later and to then unregister
the acpi_video backlight device(s).

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/acpi_video.c   |  2 --
 drivers/acpi/video_detect.c | 36 ------------------------------------
 2 files changed, 38 deletions(-)

diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
index 09dd86f86cf3..d1e41f30c004 100644
--- a/drivers/acpi/acpi_video.c
+++ b/drivers/acpi/acpi_video.c
@@ -94,7 +94,6 @@ static void acpi_video_bus_notify(struct acpi_device *device,
u32 event);
 static void acpi_video_bus_register_backlight_work(struct work_struct
*ignored);
 static DECLARE_DELAYED_WORK(video_bus_register_backlight_work,
 			    acpi_video_bus_register_backlight_work);
-void acpi_video_detect_exit(void);
 
 /*
  * Indices in the _BCL method response: the first two items are special,
@@ -2342,7 +2341,6 @@ static int __init acpi_video_init(void)
 
 static void __exit acpi_video_exit(void)
 {
-	acpi_video_detect_exit();
 	acpi_video_unregister();
 }
 
diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index 385eb49c763f..fb49b8f4523a 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -38,10 +38,6 @@
 
 void acpi_video_unregister_backlight(void);
 
-static bool backlight_notifier_registered;
-static struct notifier_block backlight_nb;
-static struct work_struct backlight_notify_work;
-
 static enum acpi_backlight_type acpi_backlight_cmdline = acpi_backlight_undef;
 static enum acpi_backlight_type acpi_backlight_dmi = acpi_backlight_undef;
 
@@ -538,26 +534,6 @@ static const struct dmi_system_id video_detect_dmi_table[]
= {
 	{ },
 };
 
-/* This uses a workqueue to avoid various locking ordering issues */
-static void acpi_video_backlight_notify_work(struct work_struct *work)
-{
-	if (acpi_video_get_backlight_type() != acpi_backlight_video)
-		acpi_video_unregister_backlight();
-}
-
-static int acpi_video_backlight_notify(struct notifier_block *nb,
-				       unsigned long val, void *bd)
-{
-	struct backlight_device *backlight = bd;
-
-	/* A raw bl registering may change video -> native */
-	if (backlight->props.type == BACKLIGHT_RAW &&
-	    val == BACKLIGHT_REGISTERED)
-		schedule_work(&backlight_notify_work);
-
-	return NOTIFY_OK;
-}
-
 /*
  * Determine which type of backlight interface to use on this system,
  * First check cmdline, then dmi quirks, then do autodetect.
@@ -587,12 +563,6 @@ static enum acpi_backlight_type
__acpi_video_get_backlight_type(bool native)
 		acpi_walk_namespace(ACPI_TYPE_DEVICE, ACPI_ROOT_OBJECT,
 				    ACPI_UINT32_MAX, find_video, NULL,
 				    &video_caps, NULL);
-		INIT_WORK(&backlight_notify_work,
-			  acpi_video_backlight_notify_work);
-		backlight_nb.notifier_call = acpi_video_backlight_notify;
-		backlight_nb.priority = 0;
-		if (backlight_register_notifier(&backlight_nb) == 0)
-			backlight_notifier_registered = true;
 		init_done = true;
 	}
 	if (native)
@@ -639,9 +609,3 @@ void acpi_video_set_dmi_backlight_type(enum
acpi_backlight_type type)
 		acpi_video_unregister_backlight();
 }
 EXPORT_SYMBOL(acpi_video_set_dmi_backlight_type);
-
-void __exit acpi_video_detect_exit(void)
-{
-	if (backlight_notifier_registered)
-		backlight_unregister_notifier(&backlight_nb);
-}
-- 
2.37.2

On machins without an i915 opregion the acpi_video driver immediately
probes the ACPI video bus and used to also immediately register
acpi_video# backlight devices when supported.

Once the drm/kms driver then loaded later and possibly registered
a native backlight device then the drivers/acpi/video_detect.c code
unregistered the acpi_video0 device to avoid there being 2 backlight
devices (when acpi_video_get_backlight_type()==native).

This means that userspace used to briefly see 2 devices and the
disappearing of acpi_video0 after a brief time confuses the systemd
backlight level save/restore code, see e.g.:
https://bbs.archlinux.org/viewtopic.php?id=269920

To fix this the ACPI video code has been modified to make backlight class
device registration a separate step, relying on the drm/kms driver to
ask for the acpi_video backlight registration after it is done setting up
its native backlight device.

Add a call to the new acpi_video_register_backlight() after the i915 calls
acpi_video_register() (after setting up the i915 opregion) so that the
acpi_video backlight devices get registered on systems where the i915
native backlight device is not registered.

Changes in v2:
-Only call acpi_video_register_backlight() when a panel is detected

Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/gpu/drm/i915/display/intel_display.c | 8 ++++++++
 drivers/gpu/drm/i915/display/intel_panel.c   | 3 +++
 drivers/gpu/drm/i915/i915_drv.h              | 2 ++
 3 files changed, 13 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c
b/drivers/gpu/drm/i915/display/intel_display.c
index 6103b02c081f..2bb53efdb149 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -9088,6 +9088,14 @@ void intel_display_driver_register(struct
drm_i915_private *i915)
 	/* Must be done after probing outputs */
 	intel_opregion_register(i915);
 	acpi_video_register();
+	/*
+	 * Only call this if i915 is driving the internal panel. If the internal
+	 * panel is not driven by i915 then another GPU driver may still register
+	 * a native backlight driver later and this should only be called after
+	 * any native backlights have been registered.
+	 */
+	if (i915->have_panel)
+		acpi_video_register_backlight();
 
 	intel_audio_init(i915);
 
diff --git a/drivers/gpu/drm/i915/display/intel_panel.c
b/drivers/gpu/drm/i915/display/intel_panel.c
index 237a40623dd7..4536c527f50c 100644
--- a/drivers/gpu/drm/i915/display/intel_panel.c
+++ b/drivers/gpu/drm/i915/display/intel_panel.c
@@ -646,8 +646,11 @@ intel_panel_mode_valid(struct intel_connector *connector,
 
 int intel_panel_init(struct intel_connector *connector)
 {
+	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
 	struct intel_panel *panel = &connector->panel;
 
+	dev_priv->have_panel = true;
+
 	intel_backlight_init_funcs(panel);
 
 	drm_dbg_kms(connector->base.dev,
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 69ce6db6a7c1..14b0dcaf25c2 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -756,6 +756,8 @@ struct drm_i915_private {
 
 	bool ipc_enabled;
 
+	bool have_panel;
+
 	struct intel_audio_private audio;
 
 	struct i915_pmu pmu;
-- 
2.37.2

Typically the acpi_video driver will initialize before nouveau, which
used to cause /sys/class/backlight/acpi_video0 to get registered and then
nouveau would register its own nv_backlight device later. After which
the drivers/acpi/video_detect.c code unregistered the acpi_video0 device
to avoid there being 2 backlight devices.

This means that userspace used to briefly see 2 devices and the
disappearing of acpi_video0 after a brief time confuses the systemd
backlight level save/restore code, see e.g.:
https://bbs.archlinux.org/viewtopic.php?id=269920

To fix this the ACPI video code has been modified to make backlight class
device registration a separate step, relying on the drm/kms driver to
ask for the acpi_video backlight registration after it is done setting up
its native backlight device.

Add a call to the new acpi_video_register_backlight() when native backlight
device registration has failed / was skipped to ensure that there is a
backlight device available before the drm_device gets registered with
userspace.

Changes in v2:
- Add nouveau_acpi_video_register_backlight() wrapper to avoid unresolved
  symbol errors on non X86

Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/gpu/drm/nouveau/nouveau_acpi.c      | 5 +++++
 drivers/gpu/drm/nouveau/nouveau_acpi.h      | 2 ++
 drivers/gpu/drm/nouveau/nouveau_backlight.c | 7 +++++++
 3 files changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/nouveau_acpi.c
b/drivers/gpu/drm/nouveau/nouveau_acpi.c
index 1592c9cd7750..8cf096f841a9 100644
--- a/drivers/gpu/drm/nouveau/nouveau_acpi.c
+++ b/drivers/gpu/drm/nouveau/nouveau_acpi.c
@@ -391,3 +391,8 @@ bool nouveau_acpi_video_backlight_use_native(void)
 {
 	return acpi_video_backlight_use_native();
 }
+
+void nouveau_acpi_video_register_backlight(void)
+{
+	acpi_video_register_backlight();
+}
diff --git a/drivers/gpu/drm/nouveau/nouveau_acpi.h
b/drivers/gpu/drm/nouveau/nouveau_acpi.h
index 3c666c30dfca..e39dd8b94b8b 100644
--- a/drivers/gpu/drm/nouveau/nouveau_acpi.h
+++ b/drivers/gpu/drm/nouveau/nouveau_acpi.h
@@ -12,6 +12,7 @@ void nouveau_unregister_dsm_handler(void);
 void nouveau_switcheroo_optimus_dsm(void);
 void *nouveau_acpi_edid(struct drm_device *, struct drm_connector *);
 bool nouveau_acpi_video_backlight_use_native(void);
+void nouveau_acpi_video_register_backlight(void);
 #else
 static inline bool nouveau_is_optimus(void) { return false; };
 static inline bool nouveau_is_v1_dsm(void) { return false; };
@@ -20,6 +21,7 @@ static inline void nouveau_unregister_dsm_handler(void) {}
 static inline void nouveau_switcheroo_optimus_dsm(void) {}
 static inline void *nouveau_acpi_edid(struct drm_device *dev, struct
drm_connector *connector) { return NULL; }
 static inline bool nouveau_acpi_video_backlight_use_native(void) { return true;
}
+static inline void nouveau_acpi_video_register_backlight(void) {}
 #endif
 
 #endif
diff --git a/drivers/gpu/drm/nouveau/nouveau_backlight.c
b/drivers/gpu/drm/nouveau/nouveau_backlight.c
index d2b8f8c13db4..a614582779ca 100644
--- a/drivers/gpu/drm/nouveau/nouveau_backlight.c
+++ b/drivers/gpu/drm/nouveau/nouveau_backlight.c
@@ -436,6 +436,13 @@ nouveau_backlight_init(struct drm_connector *connector)
 
 fail_alloc:
 	kfree(bl);
+	/*
+	 * If we get here we have an internal panel, but no nv_backlight,
+	 * try registering an ACPI video backlight device instead.
+	 */
+	if (ret == 0)
+		nouveau_acpi_video_register_backlight();
+
 	return ret;
 }
 
-- 
2.37.2

Typically the acpi_video driver will initialize before amdgpu, which
used to cause /sys/class/backlight/acpi_video0 to get registered and then
amdgpu would register its own amdgpu_bl# device later. After which
the drivers/acpi/video_detect.c code unregistered the acpi_video0 device
to avoid there being 2 backlight devices.

This means that userspace used to briefly see 2 devices and the
disappearing of acpi_video0 after a brief time confuses the systemd
backlight level save/restore code, see e.g.:
https://bbs.archlinux.org/viewtopic.php?id=269920

To fix this the ACPI video code has been modified to make backlight class
device registration a separate step, relying on the drm/kms driver to
ask for the acpi_video backlight registration after it is done setting up
its native backlight device.

Add a call to the new acpi_video_register_backlight() when amdgpu skips
registering its own backlight device because of either the firmware_flags
or the acpi_video_get_backlight_type() return value. This ensures that
if the acpi_video backlight device should be used, it will be available
before the amdgpu drm_device gets registered with userspace.

Acked-by: Alex Deucher <alexander.deucher at amd.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/gpu/drm/amd/amdgpu/atombios_encoders.c    | 9 +++++++--
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 ++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c
b/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c
index b4e3cedceaf8..6be9ac2b9c5b 100644
--- a/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c
+++ b/drivers/gpu/drm/amd/amdgpu/atombios_encoders.c
@@ -184,11 +184,11 @@ void amdgpu_atombios_encoder_init_backlight(struct
amdgpu_encoder *amdgpu_encode
 		return;
 
 	if (!(adev->mode_info.firmware_flags &
ATOM_BIOS_INFO_BL_CONTROLLED_BY_GPU))
-		return;
+		goto register_acpi_backlight;
 
 	if (!acpi_video_backlight_use_native()) {
 		drm_info(dev, "Skipping amdgpu atom DIG backlight registration\n");
-		return;
+		goto register_acpi_backlight;
 	}
 
 	pdata = kmalloc(sizeof(struct amdgpu_backlight_privdata), GFP_KERNEL);
@@ -225,6 +225,11 @@ void amdgpu_atombios_encoder_init_backlight(struct
amdgpu_encoder *amdgpu_encode
 error:
 	kfree(pdata);
 	return;
+
+register_acpi_backlight:
+	/* Try registering an ACPI video backlight device instead. */
+	acpi_video_register_backlight();
+	return;
 }
 
 void
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 706c67f4bda8..c450964f84d4 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -4037,6 +4037,8 @@ amdgpu_dm_register_backlight_device(struct
amdgpu_display_manager *dm)
 
 	if (!acpi_video_backlight_use_native()) {
 		drm_info(adev_to_drm(dm->adev), "Skipping amdgpu DM backlight
registration\n");
+		/* Try registering an ACPI video backlight device instead. */
+		acpi_video_register_backlight();
 		return;
 	}
 
-- 
2.37.2

Typically the acpi_video driver will initialize before radeon, which
used to cause /sys/class/backlight/acpi_video0 to get registered and then
radeon would register its own radeon_bl# device later. After which
the drivers/acpi/video_detect.c code unregistered the acpi_video0 device
to avoid there being 2 backlight devices.

This means that userspace used to briefly see 2 devices and the
disappearing of acpi_video0 after a brief time confuses the systemd
backlight level save/restore code, see e.g.:
https://bbs.archlinux.org/viewtopic.php?id=269920

To fix this the ACPI video code has been modified to make backlight class
device registration a separate step, relying on the drm/kms driver to
ask for the acpi_video backlight registration after it is done setting up
its native backlight device.

Add a call to the new acpi_video_register_backlight() when radeon skips
registering its own backlight device because of e.g. the firmware_flags
or the acpi_video_get_backlight_type() return value. This ensures that
if the acpi_video backlight device should be used, it will be available
before the radeon drm_device gets registered with userspace.

Acked-by: Alex Deucher <alexander.deucher at amd.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/gpu/drm/radeon/radeon_encoders.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/radeon/radeon_encoders.c
b/drivers/gpu/drm/radeon/radeon_encoders.c
index 35c535e48b8d..fbc0a2182318 100644
--- a/drivers/gpu/drm/radeon/radeon_encoders.c
+++ b/drivers/gpu/drm/radeon/radeon_encoders.c
@@ -30,6 +30,8 @@
 #include <drm/drm_device.h>
 #include <drm/radeon_drm.h>
 
+#include <acpi/video.h>
+
 #include "radeon.h"
 #include "radeon_atombios.h"
 #include "radeon_legacy_encoders.h"
@@ -167,7 +169,7 @@ static void radeon_encoder_add_backlight(struct
radeon_encoder *radeon_encoder,
 		return;
 
 	if (radeon_backlight == 0) {
-		return;
+		use_bl = false;
 	} else if (radeon_backlight == 1) {
 		use_bl = true;
 	} else if (radeon_backlight == -1) {
@@ -193,6 +195,13 @@ static void radeon_encoder_add_backlight(struct
radeon_encoder *radeon_encoder,
 		else
 			radeon_legacy_backlight_init(radeon_encoder, connector);
 	}
+
+	/*
+	 * If there is no native backlight device (which may happen even when
+	 * use_bl==true) try registering an ACPI video backlight device instead.
+	 */
+	if (!rdev->mode_info.bl_encoder)
+		acpi_video_register_backlight();
 }
 
 void
-- 
2.37.2

Move the WMI interface definitions to a header, so that the definitions
can be shared with drivers/acpi/video_detect.c .

Changes in v2:
- Add missing Nvidia copyright header
- Move WMI_BRIGHTNESS_GUID to nvidia-wmi-ec-backlight.h as well

Suggested-by: Daniel Dadap <ddadap at nvidia.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 MAINTAINERS                                   |  1 +
 .../platform/x86/nvidia-wmi-ec-backlight.c    | 68 +----------------
 .../x86/nvidia-wmi-ec-backlight.h             | 76 +++++++++++++++++++
 3 files changed, 78 insertions(+), 67 deletions(-)
 create mode 100644 include/linux/platform_data/x86/nvidia-wmi-ec-backlight.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 9d7f64dc0efe..d6f6b96f51f7 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -14527,6 +14527,7 @@ M:	Daniel Dadap <ddadap at nvidia.com>
 L:	platform-driver-x86 at vger.kernel.org
 S:	Supported
 F:	drivers/platform/x86/nvidia-wmi-ec-backlight.c
+F:	include/linux/platform_data/x86/nvidia-wmi-ec-backlight.h
 
 NVM EXPRESS DRIVER
 M:	Keith Busch <kbusch at kernel.org>
diff --git a/drivers/platform/x86/nvidia-wmi-ec-backlight.c
b/drivers/platform/x86/nvidia-wmi-ec-backlight.c
index 61e37194df70..be803e47eac0 100644
--- a/drivers/platform/x86/nvidia-wmi-ec-backlight.c
+++ b/drivers/platform/x86/nvidia-wmi-ec-backlight.c
@@ -7,74 +7,10 @@
 #include <linux/backlight.h>
 #include <linux/mod_devicetable.h>
 #include <linux/module.h>
+#include <linux/platform_data/x86/nvidia-wmi-ec-backlight.h>
 #include <linux/types.h>
 #include <linux/wmi.h>
 
-/**
- * enum wmi_brightness_method - WMI method IDs
- * @WMI_BRIGHTNESS_METHOD_LEVEL:  Get/Set EC brightness level status
- * @WMI_BRIGHTNESS_METHOD_SOURCE: Get/Set EC Brightness Source
- */
-enum wmi_brightness_method {
-	WMI_BRIGHTNESS_METHOD_LEVEL = 1,
-	WMI_BRIGHTNESS_METHOD_SOURCE = 2,
-	WMI_BRIGHTNESS_METHOD_MAX
-};
-
-/**
- * enum wmi_brightness_mode - Operation mode for WMI-wrapped method
- * @WMI_BRIGHTNESS_MODE_GET:            Get the current brightness
level/source.
- * @WMI_BRIGHTNESS_MODE_SET:            Set the brightness level.
- * @WMI_BRIGHTNESS_MODE_GET_MAX_LEVEL:  Get the maximum brightness level. This
- *                                      is only valid when the WMI method is
- *                                      %WMI_BRIGHTNESS_METHOD_LEVEL.
- */
-enum wmi_brightness_mode {
-	WMI_BRIGHTNESS_MODE_GET = 0,
-	WMI_BRIGHTNESS_MODE_SET = 1,
-	WMI_BRIGHTNESS_MODE_GET_MAX_LEVEL = 2,
-	WMI_BRIGHTNESS_MODE_MAX
-};
-
-/**
- * enum wmi_brightness_source - Backlight brightness control source selection
- * @WMI_BRIGHTNESS_SOURCE_GPU: Backlight brightness is controlled by the GPU.
- * @WMI_BRIGHTNESS_SOURCE_EC:  Backlight brightness is controlled by the
- *                             system's Embedded Controller (EC).
- * @WMI_BRIGHTNESS_SOURCE_AUX: Backlight brightness is controlled over the
- *                             DisplayPort AUX channel.
- */
-enum wmi_brightness_source {
-	WMI_BRIGHTNESS_SOURCE_GPU = 1,
-	WMI_BRIGHTNESS_SOURCE_EC = 2,
-	WMI_BRIGHTNESS_SOURCE_AUX = 3,
-	WMI_BRIGHTNESS_SOURCE_MAX
-};
-
-/**
- * struct wmi_brightness_args - arguments for the WMI-wrapped ACPI method
- * @mode:    Pass in an &enum wmi_brightness_mode value to select between
- *           getting or setting a value.
- * @val:     In parameter for value to set when using %WMI_BRIGHTNESS_MODE_SET
- *           mode. Not used in conjunction with %WMI_BRIGHTNESS_MODE_GET or
- *           %WMI_BRIGHTNESS_MODE_GET_MAX_LEVEL mode.
- * @ret:     Out parameter returning retrieved value when operating in
- *           %WMI_BRIGHTNESS_MODE_GET or %WMI_BRIGHTNESS_MODE_GET_MAX_LEVEL
- *           mode. Not used in %WMI_BRIGHTNESS_MODE_SET mode.
- * @ignored: Padding; not used. The ACPI method expects a 24 byte params
struct.
- *
- * This is the parameters structure for the WmiBrightnessNotify ACPI method as
- * wrapped by WMI. The value passed in to @val or returned by @ret will be a
- * brightness value when the WMI method ID is %WMI_BRIGHTNESS_METHOD_LEVEL, or
- * an &enum wmi_brightness_source value with %WMI_BRIGHTNESS_METHOD_SOURCE.
- */
-struct wmi_brightness_args {
-	u32 mode;
-	u32 val;
-	u32 ret;
-	u32 ignored[3];
-};
-
 /**
  * wmi_brightness_notify() - helper function for calling WMI-wrapped ACPI
method
  * @w:    Pointer to the struct wmi_device identified by %WMI_BRIGHTNESS_GUID
@@ -191,8 +127,6 @@ static int nvidia_wmi_ec_backlight_probe(struct wmi_device
*wdev, const void *ct
 	return PTR_ERR_OR_ZERO(bdev);
 }
 
-#define WMI_BRIGHTNESS_GUID "603E9613-EF25-4338-A3D0-C46177516DB7"
-
 static const struct wmi_device_id nvidia_wmi_ec_backlight_id_table[] = {
 	{ .guid_string = WMI_BRIGHTNESS_GUID },
 	{ }
diff --git a/include/linux/platform_data/x86/nvidia-wmi-ec-backlight.h
b/include/linux/platform_data/x86/nvidia-wmi-ec-backlight.h
new file mode 100644
index 000000000000..23d60130272c
--- /dev/null
+++ b/include/linux/platform_data/x86/nvidia-wmi-ec-backlight.h
@@ -0,0 +1,76 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2020, NVIDIA CORPORATION.  All rights reserved.
+ */
+
+#ifndef __PLATFORM_DATA_X86_NVIDIA_WMI_EC_BACKLIGHT_H
+#define __PLATFORM_DATA_X86_NVIDIA_WMI_EC_BACKLIGHT_H
+
+#define WMI_BRIGHTNESS_GUID "603E9613-EF25-4338-A3D0-C46177516DB7"
+
+/**
+ * enum wmi_brightness_method - WMI method IDs
+ * @WMI_BRIGHTNESS_METHOD_LEVEL:  Get/Set EC brightness level status
+ * @WMI_BRIGHTNESS_METHOD_SOURCE: Get/Set EC Brightness Source
+ */
+enum wmi_brightness_method {
+	WMI_BRIGHTNESS_METHOD_LEVEL = 1,
+	WMI_BRIGHTNESS_METHOD_SOURCE = 2,
+	WMI_BRIGHTNESS_METHOD_MAX
+};
+
+/**
+ * enum wmi_brightness_mode - Operation mode for WMI-wrapped method
+ * @WMI_BRIGHTNESS_MODE_GET:            Get the current brightness
level/source.
+ * @WMI_BRIGHTNESS_MODE_SET:            Set the brightness level.
+ * @WMI_BRIGHTNESS_MODE_GET_MAX_LEVEL:  Get the maximum brightness level. This
+ *                                      is only valid when the WMI method is
+ *                                      %WMI_BRIGHTNESS_METHOD_LEVEL.
+ */
+enum wmi_brightness_mode {
+	WMI_BRIGHTNESS_MODE_GET = 0,
+	WMI_BRIGHTNESS_MODE_SET = 1,
+	WMI_BRIGHTNESS_MODE_GET_MAX_LEVEL = 2,
+	WMI_BRIGHTNESS_MODE_MAX
+};
+
+/**
+ * enum wmi_brightness_source - Backlight brightness control source selection
+ * @WMI_BRIGHTNESS_SOURCE_GPU: Backlight brightness is controlled by the GPU.
+ * @WMI_BRIGHTNESS_SOURCE_EC:  Backlight brightness is controlled by the
+ *                             system's Embedded Controller (EC).
+ * @WMI_BRIGHTNESS_SOURCE_AUX: Backlight brightness is controlled over the
+ *                             DisplayPort AUX channel.
+ */
+enum wmi_brightness_source {
+	WMI_BRIGHTNESS_SOURCE_GPU = 1,
+	WMI_BRIGHTNESS_SOURCE_EC = 2,
+	WMI_BRIGHTNESS_SOURCE_AUX = 3,
+	WMI_BRIGHTNESS_SOURCE_MAX
+};
+
+/**
+ * struct wmi_brightness_args - arguments for the WMI-wrapped ACPI method
+ * @mode:    Pass in an &enum wmi_brightness_mode value to select between
+ *           getting or setting a value.
+ * @val:     In parameter for value to set when using %WMI_BRIGHTNESS_MODE_SET
+ *           mode. Not used in conjunction with %WMI_BRIGHTNESS_MODE_GET or
+ *           %WMI_BRIGHTNESS_MODE_GET_MAX_LEVEL mode.
+ * @ret:     Out parameter returning retrieved value when operating in
+ *           %WMI_BRIGHTNESS_MODE_GET or %WMI_BRIGHTNESS_MODE_GET_MAX_LEVEL
+ *           mode. Not used in %WMI_BRIGHTNESS_MODE_SET mode.
+ * @ignored: Padding; not used. The ACPI method expects a 24 byte params
struct.
+ *
+ * This is the parameters structure for the WmiBrightnessNotify ACPI method as
+ * wrapped by WMI. The value passed in to @val or returned by @ret will be a
+ * brightness value when the WMI method ID is %WMI_BRIGHTNESS_METHOD_LEVEL, or
+ * an &enum wmi_brightness_source value with %WMI_BRIGHTNESS_METHOD_SOURCE.
+ */
+struct wmi_brightness_args {
+	u32 mode;
+	u32 val;
+	u32 ret;
+	u32 ignored[3];
+};
+
+#endif
-- 
2.37.2

Refactor acpi_video_get_backlight_type() so that the heuristics /
detection steps are stricly in order of descending precedence.

Also move the comments describing the steps to when the various steps are
actually done, to avoid the comments getting out of sync with the code.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/video_detect.c | 39 ++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index fb49b8f4523a..cc9d0d91e268 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -537,16 +537,6 @@ static const struct dmi_system_id video_detect_dmi_table[]
= {
 /*
  * Determine which type of backlight interface to use on this system,
  * First check cmdline, then dmi quirks, then do autodetect.
- *
- * The autodetect order is:
- * 1) Is the acpi-video backlight interface supported ->
- *  no, use a vendor interface
- * 2) Is this a win8 "ready" BIOS and do we have a native interface
->
- *  yes, use a native interface
- * 3) Else use the acpi-video interface
- *
- * Arguably the native on win8 check should be done first, but that would
- * be a behavior change, which may causes issues.
  */
 static enum acpi_backlight_type __acpi_video_get_backlight_type(bool native)
 {
@@ -569,19 +559,36 @@ static enum acpi_backlight_type
__acpi_video_get_backlight_type(bool native)
 		native_available = true;
 	mutex_unlock(&init_mutex);
 
+	/*
+	 * The below heuristics / detection steps are in order of descending
+	 * presedence. The commandline takes presedence over anything else.
+	 */
 	if (acpi_backlight_cmdline != acpi_backlight_undef)
 		return acpi_backlight_cmdline;
 
+	/* DMI quirks override any autodetection. */
 	if (acpi_backlight_dmi != acpi_backlight_undef)
 		return acpi_backlight_dmi;
 
-	if (!(video_caps & ACPI_VIDEO_BACKLIGHT))
-		return acpi_backlight_vendor;
-
-	if (acpi_osi_is_win8() && native_available)
-		return acpi_backlight_native;
+	/* On systems with ACPI video use either native or ACPI video. */
+	if (video_caps & ACPI_VIDEO_BACKLIGHT) {
+		/*
+		 * Windows 8 and newer no longer use the ACPI video interface,
+		 * so it often does not work. If the ACPI tables are written
+		 * for win8 and native brightness ctl is available, use that.
+		 *
+		 * The native check deliberately is inside the if acpi-video
+		 * block on older devices without acpi-video support native
+		 * is usually not the best choice.
+		 */
+		if (acpi_osi_is_win8() && native_available)
+			return acpi_backlight_native;
+		else
+			return acpi_backlight_video;
+	}
 
-	return acpi_backlight_video;
+	/* No ACPI video (old hw), use vendor specific fw methods. */
+	return acpi_backlight_vendor;
 }
 
 enum acpi_backlight_type acpi_video_get_backlight_type(void)
-- 
2.37.2

On some new laptop designs a new Nvidia specific WMI interface is present
which gives info about panel brightness control and may allow controlling
the brightness through this interface when the embedded controller is used
for brightness control.

When this WMI interface is present and indicates that the EC is used,
then this interface should be used for brightness control.

Changes in v2:
- Use the new shared nvidia-wmi-ec-backlight.h header for the
  WMI firmware API definitions
- ACPI_VIDEO can now be enabled on non X86 too,
  adjust the Kconfig changes to match this.

Changes in v3:
- Use WMI_BRIGHTNESS_GUID define

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/Kconfig           |  1 +
 drivers/acpi/video_detect.c    | 37 ++++++++++++++++++++++++++++++++++
 drivers/gpu/drm/gma500/Kconfig |  2 ++
 drivers/gpu/drm/i915/Kconfig   |  2 ++
 include/acpi/video.h           |  1 +
 5 files changed, 43 insertions(+)

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index 7802d8846a8d..44ad4b6bd234 100644
--- a/drivers/acpi/Kconfig
+++ b/drivers/acpi/Kconfig
@@ -212,6 +212,7 @@ config ACPI_VIDEO
 	tristate "Video"
 	depends on BACKLIGHT_CLASS_DEVICE
 	depends on INPUT
+	depends on ACPI_WMI || !X86
 	select THERMAL
 	help
 	  This driver implements the ACPI Extensions For Display Adapters
diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index cc9d0d91e268..4dc7fb865083 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -32,6 +32,7 @@
 #include <linux/dmi.h>
 #include <linux/module.h>
 #include <linux/pci.h>
+#include <linux/platform_data/x86/nvidia-wmi-ec-backlight.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
 #include <acpi/video.h>
@@ -75,6 +76,36 @@ find_video(acpi_handle handle, u32 lvl, void *context, void
**rv)
 	return AE_OK;
 }
 
+/* This depends on ACPI_WMI which is X86 only */
+#ifdef CONFIG_X86
+static bool nvidia_wmi_ec_supported(void)
+{
+	struct wmi_brightness_args args = {
+		.mode = WMI_BRIGHTNESS_MODE_GET,
+		.val = 0,
+		.ret = 0,
+	};
+	struct acpi_buffer buf = { (acpi_size)sizeof(args), &args };
+	acpi_status status;
+
+	status = wmi_evaluate_method(WMI_BRIGHTNESS_GUID, 0,
+				     WMI_BRIGHTNESS_METHOD_SOURCE, &buf, &buf);
+	if (ACPI_FAILURE(status))
+		return false;
+
+	/*
+	 * If brightness is handled by the EC then nvidia-wmi-ec-backlight
+	 * should be used, else the GPU driver(s) should be used.
+	 */
+	return args.ret == WMI_BRIGHTNESS_SOURCE_EC;
+}
+#else
+static bool nvidia_wmi_ec_supported(void)
+{
+	return false;
+}
+#endif
+
 /* Force to use vendor driver when the ACPI device is known to be
  * buggy */
 static int video_detect_force_vendor(const struct dmi_system_id *d)
@@ -541,6 +572,7 @@ static const struct dmi_system_id video_detect_dmi_table[] =
{
 static enum acpi_backlight_type __acpi_video_get_backlight_type(bool native)
 {
 	static DEFINE_MUTEX(init_mutex);
+	static bool nvidia_wmi_ec_present;
 	static bool native_available;
 	static bool init_done;
 	static long video_caps;
@@ -553,6 +585,7 @@ static enum acpi_backlight_type
__acpi_video_get_backlight_type(bool native)
 		acpi_walk_namespace(ACPI_TYPE_DEVICE, ACPI_ROOT_OBJECT,
 				    ACPI_UINT32_MAX, find_video, NULL,
 				    &video_caps, NULL);
+		nvidia_wmi_ec_present = nvidia_wmi_ec_supported();
 		init_done = true;
 	}
 	if (native)
@@ -570,6 +603,10 @@ static enum acpi_backlight_type
__acpi_video_get_backlight_type(bool native)
 	if (acpi_backlight_dmi != acpi_backlight_undef)
 		return acpi_backlight_dmi;
 
+	/* Special cases such as nvidia_wmi_ec and apple gmux. */
+	if (nvidia_wmi_ec_present)
+		return acpi_backlight_nvidia_wmi_ec;
+
 	/* On systems with ACPI video use either native or ACPI video. */
 	if (video_caps & ACPI_VIDEO_BACKLIGHT) {
 		/*
diff --git a/drivers/gpu/drm/gma500/Kconfig b/drivers/gpu/drm/gma500/Kconfig
index 0cff20265f97..807b989e3c77 100644
--- a/drivers/gpu/drm/gma500/Kconfig
+++ b/drivers/gpu/drm/gma500/Kconfig
@@ -7,6 +7,8 @@ config DRM_GMA500
 	select ACPI_VIDEO if ACPI
 	select BACKLIGHT_CLASS_DEVICE if ACPI
 	select INPUT if ACPI
+	select X86_PLATFORM_DEVICES if ACPI
+	select ACPI_WMI if ACPI
 	help
 	  Say yes for an experimental 2D KMS framebuffer driver for the
 	  Intel GMA500 (Poulsbo), Intel GMA600 (Moorestown/Oak Trail) and
diff --git a/drivers/gpu/drm/i915/Kconfig b/drivers/gpu/drm/i915/Kconfig
index 7ae3b7d67fcf..3efce05d7b57 100644
--- a/drivers/gpu/drm/i915/Kconfig
+++ b/drivers/gpu/drm/i915/Kconfig
@@ -23,6 +23,8 @@ config DRM_I915
 	# but for select to work, need to select ACPI_VIDEO's dependencies, ick
 	select BACKLIGHT_CLASS_DEVICE if ACPI
 	select INPUT if ACPI
+	select X86_PLATFORM_DEVICES if ACPI
+	select ACPI_WMI if ACPI
 	select ACPI_VIDEO if ACPI
 	select ACPI_BUTTON if ACPI
 	select SYNC_FILE
diff --git a/include/acpi/video.h b/include/acpi/video.h
index 0625806d3bbd..91578e77ac4e 100644
--- a/include/acpi/video.h
+++ b/include/acpi/video.h
@@ -48,6 +48,7 @@ enum acpi_backlight_type {
 	acpi_backlight_video,
 	acpi_backlight_vendor,
 	acpi_backlight_native,
+	acpi_backlight_nvidia_wmi_ec,
 };
 
 #if IS_ENABLED(CONFIG_ACPI_VIDEO)
-- 
2.37.2

On Apple laptops with an Apple GMUX using this for brightness control,
should take precedence of any other brightness control methods.

Add apple-gmux detection to acpi_video_get_backlight_type() using
the already existing apple_gmux_present() helper function.

This will allow removig the (ab)use of:

	acpi_video_set_dmi_backlight_type(acpi_backlight_vendor);

Inside the apple-gmux driver.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/video_detect.c | 4 ++++
 include/acpi/video.h        | 1 +
 2 files changed, 5 insertions(+)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index 4dc7fb865083..be2fc43418af 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -28,6 +28,7 @@
 
 #include <linux/export.h>
 #include <linux/acpi.h>
+#include <linux/apple-gmux.h>
 #include <linux/backlight.h>
 #include <linux/dmi.h>
 #include <linux/module.h>
@@ -607,6 +608,9 @@ static enum acpi_backlight_type
__acpi_video_get_backlight_type(bool native)
 	if (nvidia_wmi_ec_present)
 		return acpi_backlight_nvidia_wmi_ec;
 
+	if (apple_gmux_present())
+		return acpi_backlight_apple_gmux;
+
 	/* On systems with ACPI video use either native or ACPI video. */
 	if (video_caps & ACPI_VIDEO_BACKLIGHT) {
 		/*
diff --git a/include/acpi/video.h b/include/acpi/video.h
index 91578e77ac4e..dbd48cb8bd23 100644
--- a/include/acpi/video.h
+++ b/include/acpi/video.h
@@ -49,6 +49,7 @@ enum acpi_backlight_type {
 	acpi_backlight_vendor,
 	acpi_backlight_native,
 	acpi_backlight_nvidia_wmi_ec,
+	acpi_backlight_apple_gmux,
 };
 
 #if IS_ENABLED(CONFIG_ACPI_VIDEO)
-- 
2.37.2

Add an acpi_video_get_backlight_type() == acpi_backlight_nvidia_wmi_ec
check. This will make nvidia-wmi-ec-backlight properly honor the user
selecting a different backlight driver through the acpi_backlight=...
kernel commandline option.

Since the auto-detect code check for nvidia-wmi-ec-backlight in
drivers/acpi/video_detect.c already checks that the WMI advertised
brightness-source is the embedded controller, this new check makes it
unnecessary for nvidia_wmi_ec_backlight_probe() to check this itself.

Suggested-by: Daniel Dadap <ddadap at nvidia.com>
Reviewed-by: Daniel Dadap <ddadap at nvidia.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/platform/x86/Kconfig                   |  1 +
 drivers/platform/x86/nvidia-wmi-ec-backlight.c | 14 +++-----------
 2 files changed, 4 insertions(+), 11 deletions(-)

diff --git a/drivers/platform/x86/Kconfig b/drivers/platform/x86/Kconfig
index f2f98e942cf2..0cc5ac35fc57 100644
--- a/drivers/platform/x86/Kconfig
+++ b/drivers/platform/x86/Kconfig
@@ -93,6 +93,7 @@ config PEAQ_WMI
 
 config NVIDIA_WMI_EC_BACKLIGHT
 	tristate "EC Backlight Driver for Hybrid Graphics Notebook Systems"
+	depends on ACPI_VIDEO
 	depends on ACPI_WMI
 	depends on BACKLIGHT_CLASS_DEVICE
 	help
diff --git a/drivers/platform/x86/nvidia-wmi-ec-backlight.c
b/drivers/platform/x86/nvidia-wmi-ec-backlight.c
index be803e47eac0..baccdf658538 100644
--- a/drivers/platform/x86/nvidia-wmi-ec-backlight.c
+++ b/drivers/platform/x86/nvidia-wmi-ec-backlight.c
@@ -10,6 +10,7 @@
 #include <linux/platform_data/x86/nvidia-wmi-ec-backlight.h>
 #include <linux/types.h>
 #include <linux/wmi.h>
+#include <acpi/video.h>
 
 /**
  * wmi_brightness_notify() - helper function for calling WMI-wrapped ACPI
method
@@ -87,19 +88,10 @@ static int nvidia_wmi_ec_backlight_probe(struct wmi_device
*wdev, const void *ct
 {
 	struct backlight_properties props = {};
 	struct backlight_device *bdev;
-	u32 source;
 	int ret;
 
-	ret = wmi_brightness_notify(wdev, WMI_BRIGHTNESS_METHOD_SOURCE,
-	                           WMI_BRIGHTNESS_MODE_GET, &source);
-	if (ret)
-		return ret;
-
-	/*
-	 * This driver is only to be used when brightness control is handled
-	 * by the EC; otherwise, the GPU driver(s) should control brightness.
-	 */
-	if (source != WMI_BRIGHTNESS_SOURCE_EC)
+	/* drivers/acpi/video_detect.c also checks that SOURCE == EC */
+	if (acpi_video_get_backlight_type() != acpi_backlight_nvidia_wmi_ec)
 		return -ENODEV;
 
 	/*
-- 
2.37.2

Now that acpi_video_get_backlight_type() has apple-gmux detection (using
apple_gmux_present()), it is no longer necessary for the apple-gmux code
to manually remove possibly conflicting drivers.

So remove the handling for this from the apple-gmux driver.

Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/platform/x86/apple-gmux.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/platform/x86/apple-gmux.c
b/drivers/platform/x86/apple-gmux.c
index ffe98a18440b..ca33df7ea550 100644
--- a/drivers/platform/x86/apple-gmux.c
+++ b/drivers/platform/x86/apple-gmux.c
@@ -21,7 +21,6 @@
 #include <linux/delay.h>
 #include <linux/pci.h>
 #include <linux/vga_switcheroo.h>
-#include <acpi/video.h>
 #include <asm/io.h>
 
 /**
@@ -694,7 +693,6 @@ static int gmux_probe(struct pnp_dev *pnp, const struct
pnp_device_id *id)
 	 * backlight control and supports more levels than other options.
 	 * Disable the other backlight choices.
 	 */
-	acpi_video_set_dmi_backlight_type(acpi_backlight_vendor);
 	apple_bl_unregister();
 
 	gmux_data->power_state = VGA_SWITCHEROO_ON;
@@ -804,7 +802,6 @@ static void gmux_remove(struct pnp_dev *pnp)
 	apple_gmux_data = NULL;
 	kfree(gmux_data);
 
-	acpi_video_register();
 	apple_bl_register();
 }
 
-- 
2.37.2

acpi_video_set_dmi_backlight_type() is troublesome because it may end up
getting called after other backlight drivers have already called
acpi_video_get_backlight_type() resulting in the other drivers
already being registered even though they should not.

In case of the acpi_video backlight, acpi_video_set_dmi_backlight_type()
actually calls acpi_video_unregister_backlight() since that is often
probed earlier, leading to userspace seeing the acpi_video0 class
device being briefly available, leading to races in userspace where
udev probe-rules try to access the device and it is already gone.

In case of toshiba_acpi there are no DMI quirks to move to
acpi/video_detect.c, but it also (ab)uses it for transflective
displays. Adding transflective display support to video_detect.c would
be quite involved. But luckily there are only 2 known models with
a transflective display, so we can just add DMI quirks for those.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/video_detect.c         | 19 +++++++++++++++++++
 drivers/platform/x86/toshiba_acpi.c | 16 ----------------
 2 files changed, 19 insertions(+), 16 deletions(-)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index be2fc43418af..74e2087c8ff0 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -190,6 +190,25 @@ static const struct dmi_system_id video_detect_dmi_table[]
= {
 		},
 	},
 
+	/*
+	 * Toshiba models with Transflective display, these need to use
+	 * the toshiba_acpi vendor driver for proper Transflective handling.
+	 */
+	{
+	 .callback = video_detect_force_vendor,
+	 .matches = {
+		DMI_MATCH(DMI_SYS_VENDOR, "TOSHIBA"),
+		DMI_MATCH(DMI_PRODUCT_NAME, "PORTEGE R500"),
+		},
+	},
+	{
+	 .callback = video_detect_force_vendor,
+	 .matches = {
+		DMI_MATCH(DMI_SYS_VENDOR, "TOSHIBA"),
+		DMI_MATCH(DMI_PRODUCT_NAME, "PORTEGE R600"),
+		},
+	},
+
 	/*
 	 * These models have a working acpi_video backlight control, and using
 	 * native backlight causes a regression where backlight does not work
diff --git a/drivers/platform/x86/toshiba_acpi.c
b/drivers/platform/x86/toshiba_acpi.c
index 0fc9e8b8827b..030dc37d50b8 100644
--- a/drivers/platform/x86/toshiba_acpi.c
+++ b/drivers/platform/x86/toshiba_acpi.c
@@ -271,14 +271,6 @@ static const struct key_entry toshiba_acpi_alt_keymap[] = {
 	{ KE_END, 0 },
 };
 
-/*
- * List of models which have a broken acpi-video backlight interface and thus
- * need to use the toshiba (vendor) interface instead.
- */
-static const struct dmi_system_id toshiba_vendor_backlight_dmi[] = {
-	{}
-};
-
 /*
  * Utility
  */
@@ -2881,14 +2873,6 @@ static int toshiba_acpi_setup_backlight(struct
toshiba_acpi_dev *dev)
 		return 0;
 	}
 
-	/*
-	 * Tell acpi-video-detect code to prefer vendor backlight on all
-	 * systems with transflective backlight and on dmi matched systems.
-	 */
-	if (dev->tr_backlight_supported ||
-	    dmi_check_system(toshiba_vendor_backlight_dmi))
-		acpi_video_set_dmi_backlight_type(acpi_backlight_vendor);
-
 	if (acpi_video_get_backlight_type() != acpi_backlight_vendor)
 		return 0;
 
-- 
2.37.2

Move the backlight DMI quirks to acpi/video_detect.c, so that
the driver no longer needs to call acpi_video_set_dmi_backlight_type().

acpi_video_set_dmi_backlight_type() is troublesome because it may end up
getting called after other backlight drivers have already called
acpi_video_get_backlight_type() resulting in the other drivers
already being registered even though they should not.

Note that even though the DMI quirk table name was video_vendor_dmi_table,
5/6 quirks were actually quirks to use the GPU native backlight.

These 5 quirks also had a callback in their dmi_system_id entry which
disabled the acer-wmi vendor driver; and any DMI match resulted in:

	acpi_video_set_dmi_backlight_type(acpi_backlight_vendor);

which disabled the acpi_video driver, so only the native driver was left.
The new entries for these 5/6 devices correctly marks these as needing
the native backlight driver.

Also note that other changes in this series change the native backlight
drivers to no longer unconditionally register their backlight. Instead
these drivers now do this check:

	if (acpi_video_get_backlight_type(false) != acpi_backlight_native)
		return 0; /* bail */

which without this patch would have broken these 5/6 "special" quirks.

Since I had to look at all the commits adding the quirks anyways, to make
sure that I understood the code correctly, I've also added links to
the various original bugzillas for these quirks to the new entries.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/video_detect.c     | 53 ++++++++++++++++++++++++++
 drivers/platform/x86/acer-wmi.c | 66 ---------------------------------
 2 files changed, 53 insertions(+), 66 deletions(-)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index 74e2087c8ff0..6a2523bc02ba 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -149,6 +149,15 @@ static const struct dmi_system_id video_detect_dmi_table[]
= {
 		DMI_MATCH(DMI_BOARD_NAME, "X360"),
 		},
 	},
+	{
+	 /* https://bugzilla.redhat.com/show_bug.cgi?id=1128309 */
+	 .callback = video_detect_force_vendor,
+	 /* Acer KAV80 */
+	 .matches = {
+		DMI_MATCH(DMI_SYS_VENDOR, "Acer"),
+		DMI_MATCH(DMI_PRODUCT_NAME, "KAV80"),
+		},
+	},
 	{
 	.callback = video_detect_force_vendor,
 	/* Asus UL30VT */
@@ -437,6 +446,41 @@ static const struct dmi_system_id video_detect_dmi_table[]
= {
 		DMI_MATCH(DMI_BOARD_NAME, "JV50"),
 		},
 	},
+	{
+	 /* https://bugzilla.redhat.com/show_bug.cgi?id=1012674 */
+	 .callback = video_detect_force_native,
+	 /* Acer Aspire 5741 */
+	 .matches = {
+		DMI_MATCH(DMI_BOARD_VENDOR, "Acer"),
+		DMI_MATCH(DMI_PRODUCT_NAME, "Aspire 5741"),
+		},
+	},
+	{
+	 /* https://bugzilla.kernel.org/show_bug.cgi?id=42993 */
+	 .callback = video_detect_force_native,
+	 /* Acer Aspire 5750 */
+	 .matches = {
+		DMI_MATCH(DMI_BOARD_VENDOR, "Acer"),
+		DMI_MATCH(DMI_PRODUCT_NAME, "Aspire 5750"),
+		},
+	},
+	{
+	 /* https://bugzilla.kernel.org/show_bug.cgi?id=42833 */
+	 .callback = video_detect_force_native,
+	 /* Acer Extensa 5235 */
+	 .matches = {
+		DMI_MATCH(DMI_BOARD_VENDOR, "Acer"),
+		DMI_MATCH(DMI_PRODUCT_NAME, "Extensa 5235"),
+		},
+	},
+	{
+	 .callback = video_detect_force_native,
+	 /* Acer TravelMate 4750 */
+	 .matches = {
+		DMI_MATCH(DMI_BOARD_VENDOR, "Acer"),
+		DMI_MATCH(DMI_PRODUCT_NAME, "TravelMate 4750"),
+		},
+	},
 	{
 	 /* https://bugzilla.kernel.org/show_bug.cgi?id=207835 */
 	 .callback = video_detect_force_native,
@@ -447,6 +491,15 @@ static const struct dmi_system_id video_detect_dmi_table[]
= {
 		DMI_MATCH(DMI_BOARD_NAME, "BA51_MV"),
 		},
 	},
+	{
+	 /* https://bugzilla.kernel.org/show_bug.cgi?id=36322 */
+	 .callback = video_detect_force_native,
+	 /* Acer TravelMate 5760 */
+	 .matches = {
+		DMI_MATCH(DMI_BOARD_VENDOR, "Acer"),
+		DMI_MATCH(DMI_PRODUCT_NAME, "TravelMate 5760"),
+		},
+	},
 	{
 	.callback = video_detect_force_native,
 	/* ASUSTeK COMPUTER INC. GA401 */
diff --git a/drivers/platform/x86/acer-wmi.c b/drivers/platform/x86/acer-wmi.c
index e0230ea0cb7e..b933a5165edb 100644
--- a/drivers/platform/x86/acer-wmi.c
+++ b/drivers/platform/x86/acer-wmi.c
@@ -643,69 +643,6 @@ static const struct dmi_system_id non_acer_quirks[]
__initconst = {
 	{}
 };
 
-static int __init
-video_set_backlight_video_vendor(const struct dmi_system_id *d)
-{
-	interface->capability &= ~ACER_CAP_BRIGHTNESS;
-	pr_info("Brightness must be controlled by generic video driver\n");
-	return 0;
-}
-
-static const struct dmi_system_id video_vendor_dmi_table[] __initconst = {
-	{
-		.callback = video_set_backlight_video_vendor,
-		.ident = "Acer TravelMate 4750",
-		.matches = {
-			DMI_MATCH(DMI_BOARD_VENDOR, "Acer"),
-			DMI_MATCH(DMI_PRODUCT_NAME, "TravelMate 4750"),
-		},
-	},
-	{
-		.callback = video_set_backlight_video_vendor,
-		.ident = "Acer Extensa 5235",
-		.matches = {
-			DMI_MATCH(DMI_BOARD_VENDOR, "Acer"),
-			DMI_MATCH(DMI_PRODUCT_NAME, "Extensa 5235"),
-		},
-	},
-	{
-		.callback = video_set_backlight_video_vendor,
-		.ident = "Acer TravelMate 5760",
-		.matches = {
-			DMI_MATCH(DMI_BOARD_VENDOR, "Acer"),
-			DMI_MATCH(DMI_PRODUCT_NAME, "TravelMate 5760"),
-		},
-	},
-	{
-		.callback = video_set_backlight_video_vendor,
-		.ident = "Acer Aspire 5750",
-		.matches = {
-			DMI_MATCH(DMI_BOARD_VENDOR, "Acer"),
-			DMI_MATCH(DMI_PRODUCT_NAME, "Aspire 5750"),
-		},
-	},
-	{
-		.callback = video_set_backlight_video_vendor,
-		.ident = "Acer Aspire 5741",
-		.matches = {
-			DMI_MATCH(DMI_BOARD_VENDOR, "Acer"),
-			DMI_MATCH(DMI_PRODUCT_NAME, "Aspire 5741"),
-		},
-	},
-	{
-		/*
-		 * Note no video_set_backlight_video_vendor, we must use the
-		 * acer interface, as there is no native backlight interface.
-		 */
-		.ident = "Acer KAV80",
-		.matches = {
-			DMI_MATCH(DMI_SYS_VENDOR, "Acer"),
-			DMI_MATCH(DMI_PRODUCT_NAME, "KAV80"),
-		},
-	},
-	{}
-};
-
 /* Find which quirks are needed for a particular vendor/ model pair */
 static void __init find_quirks(void)
 {
@@ -2477,9 +2414,6 @@ static int __init acer_wmi_init(void)
 
 	set_quirks();
 
-	if (dmi_check_system(video_vendor_dmi_table))
-		acpi_video_set_dmi_backlight_type(acpi_backlight_vendor);
-
 	if (acpi_video_get_backlight_type() != acpi_backlight_vendor)
 		interface->capability &= ~ACER_CAP_BRIGHTNESS;
 
-- 
2.37.2

Remove this check from the asus-wmi backlight handling:

	/* Some Asus desktop boards export an acpi-video backlight interface,
	   stop this from showing up */
	chassis_type = dmi_get_system_info(DMI_CHASSIS_TYPE);
	if (chassis_type && !strcmp(chassis_type, "3"))
		acpi_video_set_dmi_backlight_type(acpi_backlight_vendor);

This acpi_video_set_dmi_backlight_type(acpi_backlight_vendor) call must be
removed because other changes in this series change the native backlight
drivers to no longer unconditionally register their backlight. Instead
these drivers now do this check:

        if (acpi_video_get_backlight_type(false) != acpi_backlight_native)
                return 0; /* bail */

So leaving this in place can break things on laptops with a broken
DMI chassis-type, which would have GPU native brightness control before
the addition of the acpi_video_get_backlight_type() != native check.

Removing this should be ok now, since the ACPI video code has improved
heuristics for this itself now (which includes a chassis-type check).

Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/platform/x86/asus-wmi.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/drivers/platform/x86/asus-wmi.c b/drivers/platform/x86/asus-wmi.c
index 89b604e04d7f..301166a5697d 100644
--- a/drivers/platform/x86/asus-wmi.c
+++ b/drivers/platform/x86/asus-wmi.c
@@ -3553,7 +3553,6 @@ static int asus_wmi_add(struct platform_device *pdev)
 	struct platform_driver *pdrv = to_platform_driver(pdev->dev.driver);
 	struct asus_wmi_driver *wdrv = to_asus_wmi_driver(pdrv);
 	struct asus_wmi *asus;
-	const char *chassis_type;
 	acpi_status status;
 	int err;
 	u32 result;
@@ -3635,12 +3634,6 @@ static int asus_wmi_add(struct platform_device *pdev)
 	if (asus->driver->quirks->wmi_force_als_set)
 		asus_wmi_set_als();
 
-	/* Some Asus desktop boards export an acpi-video backlight interface,
-	   stop this from showing up */
-	chassis_type = dmi_get_system_info(DMI_CHASSIS_TYPE);
-	if (chassis_type && !strcmp(chassis_type, "3"))
-		acpi_video_set_dmi_backlight_type(acpi_backlight_vendor);
-
 	if (asus->driver->quirks->wmi_backlight_power)
 		acpi_video_set_dmi_backlight_type(acpi_backlight_vendor);
 
-- 
2.37.2

Remove the asus-wmi quirk_entry.wmi_backlight_power quirk-flag, which
called acpi_video_set_dmi_backlight_type(acpi_backlight_vendor) and replace
it with acpi/video_detect.c video_detect_dmi_table[] entries using the
video_detect_force_vendor callback.

acpi_video_set_dmi_backlight_type() is troublesome because it may end up
getting called after other backlight drivers have already called
acpi_video_get_backlight_type() resulting in the other drivers
already being registered even though they should not.

Note no entries are dropped from the dmi_system_id table in asus-nb-wmi.c.
This is because the entries using the removed wmi_backlight_power flag
also use other model specific quirks from the asus-wmi quirk_entry struct.
So the quirk_asus_x55u struct and the entries pointing to it cannot be
dropped.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/video_detect.c        | 40 ++++++++++++++++++++++++++++++
 drivers/platform/x86/asus-nb-wmi.c |  7 ------
 drivers/platform/x86/asus-wmi.c    |  3 ---
 drivers/platform/x86/asus-wmi.h    |  1 -
 drivers/platform/x86/eeepc-wmi.c   | 25 +------------------
 5 files changed, 41 insertions(+), 35 deletions(-)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index 6a2523bc02ba..d893313fe1a0 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -174,6 +174,46 @@ static const struct dmi_system_id video_detect_dmi_table[]
= {
 		DMI_MATCH(DMI_PRODUCT_NAME, "UL30A"),
 		},
 	},
+	{
+	 .callback = video_detect_force_vendor,
+	 /* Asus X55U */
+	 .matches = {
+		DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
+		DMI_MATCH(DMI_PRODUCT_NAME, "X55U"),
+		},
+	},
+	{
+	 .callback = video_detect_force_vendor,
+	 /* Asus X101CH */
+	 .matches = {
+		DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
+		DMI_MATCH(DMI_PRODUCT_NAME, "X101CH"),
+		},
+	},
+	{
+	 .callback = video_detect_force_vendor,
+	 /* Asus X401U */
+	 .matches = {
+		DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
+		DMI_MATCH(DMI_PRODUCT_NAME, "X401U"),
+		},
+	},
+	{
+	 .callback = video_detect_force_vendor,
+	 /* Asus X501U */
+	 .matches = {
+		DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
+		DMI_MATCH(DMI_PRODUCT_NAME, "X501U"),
+		},
+	},
+	{
+	 .callback = video_detect_force_vendor,
+	 /* Asus 1015CX */
+	 .matches = {
+		DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
+		DMI_MATCH(DMI_PRODUCT_NAME, "1015CX"),
+		},
+	},
 	{
 	.callback = video_detect_force_vendor,
 	/* GIGABYTE GB-BXBT-2807 */
diff --git a/drivers/platform/x86/asus-nb-wmi.c
b/drivers/platform/x86/asus-nb-wmi.c
index 478dd300b9c9..810a94557a85 100644
--- a/drivers/platform/x86/asus-nb-wmi.c
+++ b/drivers/platform/x86/asus-nb-wmi.c
@@ -79,12 +79,10 @@ static struct quirk_entry quirk_asus_q500a = {
 
 /*
  * For those machines that need software to control bt/wifi status
- * and can't adjust brightness through ACPI interface
  * and have duplicate events(ACPI and WMI) for display toggle
  */
 static struct quirk_entry quirk_asus_x55u = {
 	.wapf = 4,
-	.wmi_backlight_power = true,
 	.wmi_backlight_set_devstate = true,
 	.no_display_toggle = true,
 };
@@ -147,11 +145,6 @@ static const struct dmi_system_id asus_quirks[] = {
 			DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK Computer Inc."),
 			DMI_MATCH(DMI_PRODUCT_NAME, "U32U"),
 		},
-		/*
-		 * Note this machine has a Brazos APU, and most Brazos Asus
-		 * machines need quirk_asus_x55u / wmi_backlight_power but
-		 * here acpi-video seems to work fine for backlight control.
-		 */
 		.driver_data = &quirk_asus_wapf4,
 	},
 	{
diff --git a/drivers/platform/x86/asus-wmi.c b/drivers/platform/x86/asus-wmi.c
index 301166a5697d..5cf9d9aff164 100644
--- a/drivers/platform/x86/asus-wmi.c
+++ b/drivers/platform/x86/asus-wmi.c
@@ -3634,9 +3634,6 @@ static int asus_wmi_add(struct platform_device *pdev)
 	if (asus->driver->quirks->wmi_force_als_set)
 		asus_wmi_set_als();
 
-	if (asus->driver->quirks->wmi_backlight_power)
-		acpi_video_set_dmi_backlight_type(acpi_backlight_vendor);
-
 	if (asus->driver->quirks->wmi_backlight_native)
 		acpi_video_set_dmi_backlight_type(acpi_backlight_native);
 
diff --git a/drivers/platform/x86/asus-wmi.h b/drivers/platform/x86/asus-wmi.h
index b302415bf1d9..30770e411301 100644
--- a/drivers/platform/x86/asus-wmi.h
+++ b/drivers/platform/x86/asus-wmi.h
@@ -29,7 +29,6 @@ struct quirk_entry {
 	bool hotplug_wireless;
 	bool scalar_panel_brightness;
 	bool store_backlight_power;
-	bool wmi_backlight_power;
 	bool wmi_backlight_native;
 	bool wmi_backlight_set_devstate;
 	bool wmi_force_als_set;
diff --git a/drivers/platform/x86/eeepc-wmi.c b/drivers/platform/x86/eeepc-wmi.c
index ce86d84ee796..32d9f0ba6be3 100644
--- a/drivers/platform/x86/eeepc-wmi.c
+++ b/drivers/platform/x86/eeepc-wmi.c
@@ -96,11 +96,6 @@ static struct quirk_entry quirk_asus_et2012_type3 = {
 	.store_backlight_power = true,
 };
 
-static struct quirk_entry quirk_asus_x101ch = {
-	/* We need this when ACPI function doesn't do this well */
-	.wmi_backlight_power = true,
-};
-
 static struct quirk_entry *quirks;
 
 static void et2012_quirks(void)
@@ -151,25 +146,7 @@ static const struct dmi_system_id asus_quirks[] = {
 		},
 		.driver_data = &quirk_asus_unknown,
 	},
-	{
-		.callback = dmi_matched,
-		.ident = "ASUSTeK Computer INC. X101CH",
-		.matches = {
-			DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
-			DMI_MATCH(DMI_PRODUCT_NAME, "X101CH"),
-		},
-		.driver_data = &quirk_asus_x101ch,
-	},
-	{
-		.callback = dmi_matched,
-		.ident = "ASUSTeK Computer INC. 1015CX",
-		.matches = {
-			DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
-			DMI_MATCH(DMI_PRODUCT_NAME, "1015CX"),
-		},
-		.driver_data = &quirk_asus_x101ch,
-	},
-	{},
+	{}
 };
 
 static void eeepc_wmi_key_filter(struct asus_wmi_driver *asus_wmi, int *code,
-- 
2.37.2

Remove the asus-wmi quirk_entry.wmi_backlight_native quirk-flag, which
called acpi_video_set_dmi_backlight_type(acpi_backlight_native) and replace
it with acpi/video_detect.c video_detect_dmi_table[] entries using the
video_detect_force_native callback.

acpi_video_set_dmi_backlight_type() is troublesome because it may end up
getting called after other backlight drivers have already called
acpi_video_get_backlight_type() resulting in the other drivers
already being registered even though they should not.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/video_detect.c        |  8 ++++++++
 drivers/platform/x86/asus-nb-wmi.c | 14 --------------
 drivers/platform/x86/asus-wmi.c    |  3 ---
 drivers/platform/x86/asus-wmi.h    |  1 -
 4 files changed, 8 insertions(+), 18 deletions(-)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index d893313fe1a0..a09089e7fada 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -564,6 +564,14 @@ static const struct dmi_system_id video_detect_dmi_table[]
= {
 		DMI_MATCH(DMI_PRODUCT_NAME, "GA503"),
 		},
 	},
+	{
+	 .callback = video_detect_force_native,
+	 /* Asus UX303UB */
+	 .matches = {
+		DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
+		DMI_MATCH(DMI_PRODUCT_NAME, "UX303UB"),
+		},
+	},
 	/*
 	 * Clevo NL5xRU and NL5xNU/TUXEDO Aura 15 Gen1 and Gen2 have both a
 	 * working native and video interface. However the default detection
diff --git a/drivers/platform/x86/asus-nb-wmi.c
b/drivers/platform/x86/asus-nb-wmi.c
index 810a94557a85..bbfed85051ee 100644
--- a/drivers/platform/x86/asus-nb-wmi.c
+++ b/drivers/platform/x86/asus-nb-wmi.c
@@ -97,11 +97,6 @@ static struct quirk_entry quirk_asus_x200ca = {
 	.wmi_backlight_set_devstate = true,
 };
 
-static struct quirk_entry quirk_asus_ux303ub = {
-	.wmi_backlight_native = true,
-	.wmi_backlight_set_devstate = true,
-};
-
 static struct quirk_entry quirk_asus_x550lb = {
 	.wmi_backlight_set_devstate = true,
 	.xusb2pr = 0x01D9,
@@ -372,15 +367,6 @@ static const struct dmi_system_id asus_quirks[] = {
 		},
 		.driver_data = &quirk_asus_x200ca,
 	},
-	{
-		.callback = dmi_matched,
-		.ident = "ASUSTeK COMPUTER INC. UX303UB",
-		.matches = {
-			DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
-			DMI_MATCH(DMI_PRODUCT_NAME, "UX303UB"),
-		},
-		.driver_data = &quirk_asus_ux303ub,
-	},
 	{
 		.callback = dmi_matched,
 		.ident = "ASUSTeK COMPUTER INC. UX330UAK",
diff --git a/drivers/platform/x86/asus-wmi.c b/drivers/platform/x86/asus-wmi.c
index 5cf9d9aff164..434249ac47a5 100644
--- a/drivers/platform/x86/asus-wmi.c
+++ b/drivers/platform/x86/asus-wmi.c
@@ -3634,9 +3634,6 @@ static int asus_wmi_add(struct platform_device *pdev)
 	if (asus->driver->quirks->wmi_force_als_set)
 		asus_wmi_set_als();
 
-	if (asus->driver->quirks->wmi_backlight_native)
-		acpi_video_set_dmi_backlight_type(acpi_backlight_native);
-
 	if (asus->driver->quirks->xusb2pr)
 		asus_wmi_set_xusb2pr(asus);
 
diff --git a/drivers/platform/x86/asus-wmi.h b/drivers/platform/x86/asus-wmi.h
index 30770e411301..f30252efe1db 100644
--- a/drivers/platform/x86/asus-wmi.h
+++ b/drivers/platform/x86/asus-wmi.h
@@ -29,7 +29,6 @@ struct quirk_entry {
 	bool hotplug_wireless;
 	bool scalar_panel_brightness;
 	bool store_backlight_power;
-	bool wmi_backlight_native;
 	bool wmi_backlight_set_devstate;
 	bool wmi_force_als_set;
 	bool use_kbd_dock_devid;
-- 
2.37.2

acpi_video_set_dmi_backlight_type() is troublesome because it may end up
getting called after other backlight drivers have already called
acpi_video_get_backlight_type() resulting in the other drivers
already being registered even though they should not.

Move all the acpi_backlight=[vendor|native] quirks from samsung-laptop to
drivers/acpi/video_detect.c .

Note the X360 -> acpi_backlight=native quirk is not moved because that
already was present in drivers/acpi/video_detect.c .

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/video_detect.c           | 54 +++++++++++++++++
 drivers/platform/x86/samsung-laptop.c | 87 ---------------------------
 2 files changed, 54 insertions(+), 87 deletions(-)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index a09089e7fada..3861d4121172 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -222,6 +222,33 @@ static const struct dmi_system_id video_detect_dmi_table[]
= {
 		DMI_MATCH(DMI_PRODUCT_NAME, "GB-BXBT-2807"),
 		},
 	},
+	{
+	 .callback = video_detect_force_vendor,
+	 /* Samsung N150/N210/N220 */
+	 .matches = {
+		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
+		DMI_MATCH(DMI_PRODUCT_NAME, "N150/N210/N220"),
+		DMI_MATCH(DMI_BOARD_NAME, "N150/N210/N220"),
+		},
+	},
+	{
+	 .callback = video_detect_force_vendor,
+	 /* Samsung NF110/NF210/NF310 */
+	 .matches = {
+		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
+		DMI_MATCH(DMI_PRODUCT_NAME, "NF110/NF210/NF310"),
+		DMI_MATCH(DMI_BOARD_NAME, "NF110/NF210/NF310"),
+		},
+	},
+	{
+	 .callback = video_detect_force_vendor,
+	 /* Samsung NC210 */
+	 .matches = {
+		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
+		DMI_MATCH(DMI_PRODUCT_NAME, "NC210/NC110"),
+		DMI_MATCH(DMI_BOARD_NAME, "NC210/NC110"),
+		},
+	},
 	{
 	.callback = video_detect_force_vendor,
 	/* Sony VPCEH3U1E */
@@ -572,6 +599,33 @@ static const struct dmi_system_id video_detect_dmi_table[]
= {
 		DMI_MATCH(DMI_PRODUCT_NAME, "UX303UB"),
 		},
 	},
+	{
+	 .callback = video_detect_force_native,
+	 /* Samsung N150P */
+	 .matches = {
+		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
+		DMI_MATCH(DMI_PRODUCT_NAME, "N150P"),
+		DMI_MATCH(DMI_BOARD_NAME, "N150P"),
+		},
+	},
+	{
+	 .callback = video_detect_force_native,
+	 /* Samsung N145P/N250P/N260P */
+	 .matches = {
+		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
+		DMI_MATCH(DMI_PRODUCT_NAME, "N145P/N250P/N260P"),
+		DMI_MATCH(DMI_BOARD_NAME, "N145P/N250P/N260P"),
+		},
+	},
+	{
+	 .callback = video_detect_force_native,
+	 /* Samsung N250P */
+	 .matches = {
+		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
+		DMI_MATCH(DMI_PRODUCT_NAME, "N250P"),
+		DMI_MATCH(DMI_BOARD_NAME, "N250P"),
+		},
+	},
 	/*
 	 * Clevo NL5xRU and NL5xNU/TUXEDO Aura 15 Gen1 and Gen2 have both a
 	 * working native and video interface. However the default detection
diff --git a/drivers/platform/x86/samsung-laptop.c
b/drivers/platform/x86/samsung-laptop.c
index c187dcdf82f0..cc30cf08f32d 100644
--- a/drivers/platform/x86/samsung-laptop.c
+++ b/drivers/platform/x86/samsung-laptop.c
@@ -356,23 +356,13 @@ struct samsung_laptop {
 };
 
 struct samsung_quirks {
-	bool broken_acpi_video;
 	bool four_kbd_backlight_levels;
 	bool enable_kbd_backlight;
-	bool use_native_backlight;
 	bool lid_handling;
 };
 
 static struct samsung_quirks samsung_unknown = {};
 
-static struct samsung_quirks samsung_broken_acpi_video = {
-	.broken_acpi_video = true,
-};
-
-static struct samsung_quirks samsung_use_native_backlight = {
-	.use_native_backlight = true,
-};
-
 static struct samsung_quirks samsung_np740u3e = {
 	.four_kbd_backlight_levels = true,
 	.enable_kbd_backlight = true,
@@ -1540,76 +1530,6 @@ static const struct dmi_system_id samsung_dmi_table[]
__initconst = {
 		},
 	},
 	/* Specific DMI ids for laptop with quirks */
-	{
-	 .callback = samsung_dmi_matched,
-	 .ident = "N150P",
-	 .matches = {
-		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
-		DMI_MATCH(DMI_PRODUCT_NAME, "N150P"),
-		DMI_MATCH(DMI_BOARD_NAME, "N150P"),
-		},
-	 .driver_data = &samsung_use_native_backlight,
-	},
-	{
-	 .callback = samsung_dmi_matched,
-	 .ident = "N145P/N250P/N260P",
-	 .matches = {
-		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
-		DMI_MATCH(DMI_PRODUCT_NAME, "N145P/N250P/N260P"),
-		DMI_MATCH(DMI_BOARD_NAME, "N145P/N250P/N260P"),
-		},
-	 .driver_data = &samsung_use_native_backlight,
-	},
-	{
-	 .callback = samsung_dmi_matched,
-	 .ident = "N150/N210/N220",
-	 .matches = {
-		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
-		DMI_MATCH(DMI_PRODUCT_NAME, "N150/N210/N220"),
-		DMI_MATCH(DMI_BOARD_NAME, "N150/N210/N220"),
-		},
-	 .driver_data = &samsung_broken_acpi_video,
-	},
-	{
-	 .callback = samsung_dmi_matched,
-	 .ident = "NF110/NF210/NF310",
-	 .matches = {
-		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
-		DMI_MATCH(DMI_PRODUCT_NAME, "NF110/NF210/NF310"),
-		DMI_MATCH(DMI_BOARD_NAME, "NF110/NF210/NF310"),
-		},
-	 .driver_data = &samsung_broken_acpi_video,
-	},
-	{
-	 .callback = samsung_dmi_matched,
-	 .ident = "X360",
-	 .matches = {
-		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
-		DMI_MATCH(DMI_PRODUCT_NAME, "X360"),
-		DMI_MATCH(DMI_BOARD_NAME, "X360"),
-		},
-	 .driver_data = &samsung_broken_acpi_video,
-	},
-	{
-	 .callback = samsung_dmi_matched,
-	 .ident = "N250P",
-	 .matches = {
-		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
-		DMI_MATCH(DMI_PRODUCT_NAME, "N250P"),
-		DMI_MATCH(DMI_BOARD_NAME, "N250P"),
-		},
-	 .driver_data = &samsung_use_native_backlight,
-	},
-	{
-	 .callback = samsung_dmi_matched,
-	 .ident = "NC210",
-	 .matches = {
-		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
-		DMI_MATCH(DMI_PRODUCT_NAME, "NC210/NC110"),
-		DMI_MATCH(DMI_BOARD_NAME, "NC210/NC110"),
-		},
-	 .driver_data = &samsung_broken_acpi_video,
-	},
 	{
 	 .callback = samsung_dmi_matched,
 	 .ident = "730U3E/740U3E",
@@ -1654,15 +1574,8 @@ static int __init samsung_init(void)
 	samsung->handle_backlight = true;
 	samsung->quirks = quirks;
 
-#ifdef CONFIG_ACPI
-	if (samsung->quirks->broken_acpi_video)
-		acpi_video_set_dmi_backlight_type(acpi_backlight_vendor);
-	if (samsung->quirks->use_native_backlight)
-		acpi_video_set_dmi_backlight_type(acpi_backlight_native);
-
 	if (acpi_video_get_backlight_type() != acpi_backlight_vendor)
 		samsung->handle_backlight = false;
-#endif
 
 	ret = samsung_platform_init(samsung);
 	if (ret)
-- 
2.37.2

acpi_video_set_dmi_backlight_type() is troublesome because it may end
up getting called after other backlight drivers have already called
acpi_video_get_backlight_type() resulting in the other drivers
already being registered even though they should not.

In case of the acpi_video backlight, acpi_video_set_dmi_backlight_type()
actually calls acpi_video_unregister_backlight() since that is often
probed earlier, leading to userspace seeing the acpi_video0 class
device being briefly available, leading to races in userspace where
udev probe-rules try to access the device and it is already gone.

All callers have been fixed to no longer call it, so remove
acpi_video_set_dmi_backlight_type() now.

This means we now also no longer need acpi_video_unregister_backlight()
for the remove acpi_video backlight after it was wrongly registered hack,
so remove that too.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/acpi_video.c   | 10 ----------
 drivers/acpi/video_detect.c | 16 ----------------
 include/acpi/video.h        |  4 ----
 3 files changed, 30 deletions(-)

diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
index d1e41f30c004..a7c3d11e0dac 100644
--- a/drivers/acpi/acpi_video.c
+++ b/drivers/acpi/acpi_video.c
@@ -2296,16 +2296,6 @@ void acpi_video_register_backlight(void)
 }
 EXPORT_SYMBOL(acpi_video_register_backlight);
 
-void acpi_video_unregister_backlight(void)
-{
-	struct acpi_video_bus *video;
-
-	mutex_lock(&video_list_lock);
-	list_for_each_entry(video, &video_bus_head, entry)
-		acpi_video_bus_unregister_backlight(video);
-	mutex_unlock(&video_list_lock);
-}
-
 bool acpi_video_handles_brightness_key_presses(void)
 {
 	return may_report_brightness_keys &&
diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index 3861d4121172..67a0211c07b4 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -38,8 +38,6 @@
 #include <linux/workqueue.h>
 #include <acpi/video.h>
 
-void acpi_video_unregister_backlight(void);
-
 static enum acpi_backlight_type acpi_backlight_cmdline = acpi_backlight_undef;
 static enum acpi_backlight_type acpi_backlight_dmi = acpi_backlight_undef;
 
@@ -817,17 +815,3 @@ bool acpi_video_backlight_use_native(void)
 	return __acpi_video_get_backlight_type(true) == acpi_backlight_native;
 }
 EXPORT_SYMBOL(acpi_video_backlight_use_native);
-
-/*
- * Set the preferred backlight interface type based on DMI info.
- * This function allows DMI blacklists to be implemented by external
- * platform drivers instead of putting a big blacklist in video_detect.c
- */
-void acpi_video_set_dmi_backlight_type(enum acpi_backlight_type type)
-{
-	acpi_backlight_dmi = type;
-	/* Remove acpi-video backlight interface if it is no longer desired */
-	if (acpi_video_get_backlight_type() != acpi_backlight_video)
-		acpi_video_unregister_backlight();
-}
-EXPORT_SYMBOL(acpi_video_set_dmi_backlight_type);
diff --git a/include/acpi/video.h b/include/acpi/video.h
index dbd48cb8bd23..a275c35e5249 100644
--- a/include/acpi/video.h
+++ b/include/acpi/video.h
@@ -60,7 +60,6 @@ extern int acpi_video_get_edid(struct acpi_device *device, int
type,
 			       int device_id, void **edid);
 extern enum acpi_backlight_type acpi_video_get_backlight_type(void);
 extern bool acpi_video_backlight_use_native(void);
-extern void acpi_video_set_dmi_backlight_type(enum acpi_backlight_type type);
 /*
  * Note: The value returned by acpi_video_handles_brightness_key_presses()
  * may change over time and should not be cached.
@@ -86,9 +85,6 @@ static inline bool acpi_video_backlight_use_native(void)
 {
 	return true;
 }
-static inline void acpi_video_set_dmi_backlight_type(enum acpi_backlight_type
type)
-{
-}
 static inline bool acpi_video_handles_brightness_key_presses(void)
 {
 	return false;
-- 
2.37.2

acpi_backlight=native is the default for the "Samsung X360", but as
the comment explains the quirk was still necessary because even
briefly registering the acpi_video0 backlight; and then unregistering
it once the native driver showed up, was leading to issues.

After the "ACPI: video: Make backlight class device registration
a separate step" patch from earlier in this patch-series, we no
longer briefly register the acpi_video0 backlight on systems where
the native driver should be used.

So this is no longer an issue an the quirk is no longer needed.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/video_detect.c | 15 ---------------
 1 file changed, 15 deletions(-)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index 67a0211c07b4..af2833b57b8b 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -132,21 +132,6 @@ static int video_detect_force_none(const struct
dmi_system_id *d)
 }
 
 static const struct dmi_system_id video_detect_dmi_table[] = {
-	/* On Samsung X360, the BIOS will set a flag (VDRV) if generic
-	 * ACPI backlight device is used. This flag will definitively break
-	 * the backlight interface (even the vendor interface) until next
-	 * reboot. It's why we should prevent video.ko from being used here
-	 * and we can't rely on a later call to acpi_video_unregister().
-	 */
-	{
-	 .callback = video_detect_force_vendor,
-	 /* X360 */
-	 .matches = {
-		DMI_MATCH(DMI_SYS_VENDOR, "SAMSUNG ELECTRONICS CO., LTD."),
-		DMI_MATCH(DMI_PRODUCT_NAME, "X360"),
-		DMI_MATCH(DMI_BOARD_NAME, "X360"),
-		},
-	},
 	{
 	 /* https://bugzilla.redhat.com/show_bug.cgi?id=1128309 */
 	 .callback = video_detect_force_vendor,
-- 
2.37.2

acpi_backlight=native is the default for these, but as the comment
explains the quirk was still necessary because even briefly registering
the acpi_video0 backlight; and then unregistering it once the native
driver showed up, was leading to issues.

After the "ACPI: video: Make backlight class device registration
a separate step" patch from earlier in this patch-series, we no
longer briefly register the acpi_video0 backlight on systems where
the native driver should be used.

So this is no longer an issue an the quirks are no longer needed.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=215683
Tested-by: Werner Sembach <wse at tuxedocomputers.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/video_detect.c | 92 +------------------------------------
 1 file changed, 1 insertion(+), 91 deletions(-)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index af2833b57b8b..789d5913c178 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -609,97 +609,7 @@ static const struct dmi_system_id video_detect_dmi_table[]
= {
 		DMI_MATCH(DMI_BOARD_NAME, "N250P"),
 		},
 	},
-	/*
-	 * Clevo NL5xRU and NL5xNU/TUXEDO Aura 15 Gen1 and Gen2 have both a
-	 * working native and video interface. However the default detection
-	 * mechanism first registers the video interface before unregistering
-	 * it again and switching to the native interface during boot. This
-	 * results in a dangling SBIOS request for backlight change for some
-	 * reason, causing the backlight to switch to ~2% once per boot on the
-	 * first power cord connect or disconnect event. Setting the native
-	 * interface explicitly circumvents this buggy behaviour, by avoiding
-	 * the unregistering process.
-	 */
-	{
-	.callback = video_detect_force_native,
-	.ident = "Clevo NL5xRU",
-	.matches = {
-		DMI_MATCH(DMI_BOARD_NAME, "NL5xRU"),
-		},
-	},
-	{
-	.callback = video_detect_force_native,
-	.ident = "Clevo NL5xRU",
-	.matches = {
-		DMI_MATCH(DMI_SYS_VENDOR, "TUXEDO"),
-		DMI_MATCH(DMI_BOARD_NAME, "AURA1501"),
-		},
-	},
-	{
-	.callback = video_detect_force_native,
-	.ident = "Clevo NL5xRU",
-	.matches = {
-		DMI_MATCH(DMI_SYS_VENDOR, "TUXEDO"),
-		DMI_MATCH(DMI_BOARD_NAME, "EDUBOOK1502"),
-		},
-	},
-	{
-	.callback = video_detect_force_native,
-	.ident = "Clevo NL5xNU",
-	.matches = {
-		DMI_MATCH(DMI_BOARD_NAME, "NL5xNU"),
-		},
-	},
-	/*
-	 * The TongFang PF5PU1G, PF4NU1F, PF5NU1G, and PF5LUXG/TUXEDO BA15 Gen10,
-	 * Pulse 14/15 Gen1, and Pulse 15 Gen2 have the same problem as the Clevo
-	 * NL5xRU and NL5xNU/TUXEDO Aura 15 Gen1 and Gen2. See the description
-	 * above.
-	 */
-	{
-	.callback = video_detect_force_native,
-	.ident = "TongFang PF5PU1G",
-	.matches = {
-		DMI_MATCH(DMI_BOARD_NAME, "PF5PU1G"),
-		},
-	},
-	{
-	.callback = video_detect_force_native,
-	.ident = "TongFang PF4NU1F",
-	.matches = {
-		DMI_MATCH(DMI_BOARD_NAME, "PF4NU1F"),
-		},
-	},
-	{
-	.callback = video_detect_force_native,
-	.ident = "TongFang PF4NU1F",
-	.matches = {
-		DMI_MATCH(DMI_SYS_VENDOR, "TUXEDO"),
-		DMI_MATCH(DMI_BOARD_NAME, "PULSE1401"),
-		},
-	},
-	{
-	.callback = video_detect_force_native,
-	.ident = "TongFang PF5NU1G",
-	.matches = {
-		DMI_MATCH(DMI_BOARD_NAME, "PF5NU1G"),
-		},
-	},
-	{
-	.callback = video_detect_force_native,
-	.ident = "TongFang PF5NU1G",
-	.matches = {
-		DMI_MATCH(DMI_SYS_VENDOR, "TUXEDO"),
-		DMI_MATCH(DMI_BOARD_NAME, "PULSE1501"),
-		},
-	},
-	{
-	.callback = video_detect_force_native,
-	.ident = "TongFang PF5LUXG",
-	.matches = {
-		DMI_MATCH(DMI_BOARD_NAME, "PF5LUXG"),
-		},
-	},
+
 	/*
 	 * Desktops which falsely report a backlight and which our heuristics
 	 * for this do not catch.
-- 
2.37.2

The video_detect_dmi_table[] uses an unusual indentation for
before the ".name = ..." named struct initializers.

Instead of being indented with an extra tab compared to
the previous line's '{' these are indented to with only
a single space to allow for long DMI_MATCH() lines without
wrapping.

But over time some entries did not event have the single space
indent in front of the ".name = ..." lines.

Make things consistent by using a single space indent for these
lines everywhere.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 drivers/acpi/video_detect.c | 48 ++++++++++++++++++-------------------
 1 file changed, 24 insertions(+), 24 deletions(-)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index 789d5913c178..db2474fe58ac 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -142,17 +142,17 @@ static const struct dmi_system_id video_detect_dmi_table[]
= {
 		},
 	},
 	{
-	.callback = video_detect_force_vendor,
-	/* Asus UL30VT */
-	.matches = {
+	 .callback = video_detect_force_vendor,
+	 /* Asus UL30VT */
+	 .matches = {
 		DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK Computer Inc."),
 		DMI_MATCH(DMI_PRODUCT_NAME, "UL30VT"),
 		},
 	},
 	{
-	.callback = video_detect_force_vendor,
-	/* Asus UL30A */
-	.matches = {
+	 .callback = video_detect_force_vendor,
+	 /* Asus UL30A */
+	 .matches = {
 		DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK Computer Inc."),
 		DMI_MATCH(DMI_PRODUCT_NAME, "UL30A"),
 		},
@@ -198,9 +198,9 @@ static const struct dmi_system_id video_detect_dmi_table[] =
{
 		},
 	},
 	{
-	.callback = video_detect_force_vendor,
-	/* GIGABYTE GB-BXBT-2807 */
-	.matches = {
+	 .callback = video_detect_force_vendor,
+	 /* GIGABYTE GB-BXBT-2807 */
+	 .matches = {
 		DMI_MATCH(DMI_SYS_VENDOR, "GIGABYTE"),
 		DMI_MATCH(DMI_PRODUCT_NAME, "GB-BXBT-2807"),
 		},
@@ -233,17 +233,17 @@ static const struct dmi_system_id video_detect_dmi_table[]
= {
 		},
 	},
 	{
-	.callback = video_detect_force_vendor,
-	/* Sony VPCEH3U1E */
-	.matches = {
+	 .callback = video_detect_force_vendor,
+	 /* Sony VPCEH3U1E */
+	 .matches = {
 		DMI_MATCH(DMI_SYS_VENDOR, "Sony Corporation"),
 		DMI_MATCH(DMI_PRODUCT_NAME, "VPCEH3U1E"),
 		},
 	},
 	{
-	.callback = video_detect_force_vendor,
-	/* Xiaomi Mi Pad 2 */
-	.matches = {
+	 .callback = video_detect_force_vendor,
+	 /* Xiaomi Mi Pad 2 */
+	 .matches = {
 			DMI_MATCH(DMI_SYS_VENDOR, "Xiaomi Inc"),
 			DMI_MATCH(DMI_PRODUCT_NAME, "Mipad2"),
 		},
@@ -551,25 +551,25 @@ static const struct dmi_system_id video_detect_dmi_table[]
= {
 		},
 	},
 	{
-	.callback = video_detect_force_native,
-	/* ASUSTeK COMPUTER INC. GA401 */
-	.matches = {
+	 .callback = video_detect_force_native,
+	 /* ASUSTeK COMPUTER INC. GA401 */
+	 .matches = {
 		DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
 		DMI_MATCH(DMI_PRODUCT_NAME, "GA401"),
 		},
 	},
 	{
-	.callback = video_detect_force_native,
-	/* ASUSTeK COMPUTER INC. GA502 */
-	.matches = {
+	 .callback = video_detect_force_native,
+	 /* ASUSTeK COMPUTER INC. GA502 */
+	 .matches = {
 		DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
 		DMI_MATCH(DMI_PRODUCT_NAME, "GA502"),
 		},
 	},
 	{
-	.callback = video_detect_force_native,
-	/* ASUSTeK COMPUTER INC. GA503 */
-	.matches = {
+	 .callback = video_detect_force_native,
+	 /* ASUSTeK COMPUTER INC. GA503 */
+	 .matches = {
 		DMI_MATCH(DMI_SYS_VENDOR, "ASUSTeK COMPUTER INC."),
 		DMI_MATCH(DMI_PRODUCT_NAME, "GA503"),
 		},
-- 
2.37.2

Add an entry summarizing the discussion about dealing with brightness
control on devices with more then 1 internal panel.

The original discussion can be found here:
https://lore.kernel.org/dri-devel/20220517152331.16217-1-hdegoede at redhat.com/

Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 Documentation/gpu/todo.rst | 68 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)

diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst
index 7634c27ac562..393d218e4a0c 100644
--- a/Documentation/gpu/todo.rst
+++ b/Documentation/gpu/todo.rst
@@ -679,6 +679,74 @@ Contact: Sam Ravnborg
 
 Level: Advanced
 
+Brightness handling on devices with multiple internal panels
+===========================================================+
+On x86/ACPI devices there can be multiple backlight firmware interfaces:
+(ACPI) video, vendor specific and others. As well as direct/native (PWM)
+register programming by the KMS driver.
+
+To deal with this backlight drivers used on x86/ACPI call
+acpi_video_get_backlight_type() which has heuristics (+quirks) to select
+which backlight interface to use; and backlight drivers which do not match
+the returned type will not register themselves, so that only one backlight
+device gets registered (in a single GPU setup, see below).
+
+At the moment this more or less assumes that there will only
+be 1 (internal) panel on a system.
+
+On systems with 2 panels this may be a problem, depending on
+what interface acpi_video_get_backlight_type() selects:
+
+1. native: in this case the KMS driver is expected to know which backlight
+   device belongs to which output so everything should just work.
+2. video: this does support controlling multiple backlights, but some work
+   will need to be done to get the output <-> backlight device mapping
+
+The above assumes both panels will require the same backlight interface type.
+Things will break on systems with multiple panels where the 2 panels need
+a different type of control. E.g. one panel needs ACPI video backlight control,
+where as the other is using native backlight control. Currently in this case
+only one of the 2 required backlight devices will get registered, based on
+the acpi_video_get_backlight_type() return value.
+
+If this (theoretical) case ever shows up, then supporting this will need some
+work. A possible solution here would be to pass a device and connector-name
+to acpi_video_get_backlight_type() so that it can deal with this.
+
+Note in a way we already have a case where userspace sees 2 panels,
+in dual GPU laptop setups with a mux. On those systems we may see
+either 2 native backlight devices; or 2 native backlight devices.
+
+Userspace already has code to deal with this by detecting if the related
+panel is active (iow which way the mux between the GPU and the panels
+points) and then uses that backlight device. Userspace here very much
+assumes a single panel though. It picks only 1 of the 2 backlight devices
+and then only uses that one.
+
+Note that all userspace code (that I know off) is currently hardcoded
+to assume a single panel.
+
+Before the recent changes to not register multiple (e.g. video + native)
+/sys/class/backlight devices for a single panel (on a single GPU laptop),
+userspace would see multiple backlight devices all controlling the same
+backlight.
+
+To deal with this userspace had to always picks one preferred device under
+/sys/class/backlight and will ignore the others. So to support brightness
+control on multiple panels userspace will need to be updated too.
+
+There are plans to allow brightness control through the KMS API by adding
+a "display brightness" property to drm_connector objects for panels.
This
+solves a number of issues with the /sys/class/backlight API, including not
+being able to map a sysfs backlight device to a specific connector. Any
+userspace changes to add support for brightness control on devices with
+multiple panels really should build on top of this new KMS property.
+
+Contact: Hans de Goede
+
+Level: Advanced
+
 Outside DRM
 ========== 
-- 
2.37.2