Nouveau - Jul 2023 - [PATCH] drm/nouveau/nvkm/dp: Add hack to fix DP 1.3+ DPCD issues

Currently we use the drm_dp_dpcd_read_caps() helper in the DRM side of
nouveau in order to read the DPCD of a DP connector, which makes sure we do
the right thing and also check for extended DPCD caps. However, it turns
out we're not currently doing this on the nvkm side since we don't have
access to the drm_dp_aux structure there - which means that the DRM side of
the driver and the NVKM side can end up with different DPCD capabilities
for the same connector.

Ideally to fix this, we want to start setting up the drm_dp_aux device in
NVKM before we've made contact with the DRM side - which should be pretty
easy to accomplish (I'm already working on it!). Until then however,
let's
workaround this problem by porting a copy of drm_dp_read_dpcd_caps() into
NVKM - which should fix this issue.

Issue: https://gitlab.freedesktop.org/drm/nouveau/-/issues/211
Signed-off-by: Lyude Paul <lyude at redhat.com>
---
 drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c | 48 ++++++++++++++++++-
 1 file changed, 47 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c
b/drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c
index 40c8ea43c42f..b8ac66b4a2c4 100644
--- a/drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c
+++ b/drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c
@@ -26,6 +26,8 @@
 #include "head.h"
 #include "ior.h"
 
+#include <drm/display/drm_dp.h>
+
 #include <subdev/bios.h>
 #include <subdev/bios/init.h>
 #include <subdev/gpio.h>
@@ -634,6 +636,50 @@ nvkm_dp_enable_supported_link_rates(struct nvkm_outp *outp)
 	return outp->dp.rates != 0;
 }
 
+/* XXX: This is a big fat hack, and this is just drm_dp_read_dpcd_caps()
+ * converted to work inside nvkm. This is a temporary holdover until we start
+ * passing the drm_dp_aux device through NVKM
+ */
+static int
+nvkm_dp_read_dpcd_caps(struct nvkm_outp *outp)
+{
+	struct nvkm_i2c_aux *aux = outp->dp.aux;
+	u8 dpcd_ext[DP_RECEIVER_CAP_SIZE];
+	int ret;
+
+	ret = nvkm_rdaux(aux, DPCD_RC00_DPCD_REV, outp->dp.dpcd,
DP_RECEIVER_CAP_SIZE);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * Prior to DP1.3 the bit represented by
+	 * DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT was reserved.
+	 * If it is set DP_DPCD_REV at 0000h could be at a value less than
+	 * the true capability of the panel. The only way to check is to
+	 * then compare 0000h and 2200h.
+	 */
+	if (!(outp->dp.dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
+	      DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT))
+		return 0;
+
+	ret = nvkm_rdaux(aux, DP_DP13_DPCD_REV, dpcd_ext, sizeof(dpcd_ext));
+	if (ret < 0)
+		return ret;
+
+	if (outp->dp.dpcd[DP_DPCD_REV] > dpcd_ext[DP_DPCD_REV]) {
+		OUTP_DBG(outp, "Extended DPCD rev less than base DPCD rev (%d >
%d)\n",
+			 outp->dp.dpcd[DP_DPCD_REV], dpcd_ext[DP_DPCD_REV]);
+		return 0;
+	}
+
+	if (!memcmp(outp->dp.dpcd, dpcd_ext, sizeof(dpcd_ext)))
+		return 0;
+
+	memcpy(outp->dp.dpcd, dpcd_ext, sizeof(dpcd_ext));
+
+	return 0;
+}
+
 void
 nvkm_dp_enable(struct nvkm_outp *outp, bool auxpwr)
 {
@@ -689,7 +735,7 @@ nvkm_dp_enable(struct nvkm_outp *outp, bool auxpwr)
 			memset(outp->dp.lttpr, 0x00, sizeof(outp->dp.lttpr));
 		}
 
-		if (!nvkm_rdaux(aux, DPCD_RC00_DPCD_REV, outp->dp.dpcd,
sizeof(outp->dp.dpcd))) {
+		if (!nvkm_dp_read_dpcd_caps(outp)) {
 			const u8 rates[] = { 0x1e, 0x14, 0x0a, 0x06, 0 };
 			const u8 *rate;
 			int rate_max;
-- 
2.40.1

On Fri, Jul 7, 2023 at 11:58?PM Lyude Paul <lyude at redhat.com>
wrote:
>
> Currently we use the drm_dp_dpcd_read_caps() helper in the DRM side of
> nouveau in order to read the DPCD of a DP connector, which makes sure we do
> the right thing and also check for extended DPCD caps. However, it turns
> out we're not currently doing this on the nvkm side since we don't
have
> access to the drm_dp_aux structure there - which means that the DRM side of
> the driver and the NVKM side can end up with different DPCD capabilities
> for the same connector.
>
> Ideally to fix this, we want to start setting up the drm_dp_aux device in
> NVKM before we've made contact with the DRM side - which should be
pretty
> easy to accomplish (I'm already working on it!). Until then however,
let's
> workaround this problem by porting a copy of drm_dp_read_dpcd_caps() into
> NVKM - which should fix this issue.
>
> Issue: https://gitlab.freedesktop.org/drm/nouveau/-/issues/211
Should a Fixes: or Cc: stable tag be added so it gets backported?
> Signed-off-by: Lyude Paul <lyude at redhat.com>
> ---
>  drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c | 48 ++++++++++++++++++-
>  1 file changed, 47 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c
b/drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c
> index 40c8ea43c42f..b8ac66b4a2c4 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c
> @@ -26,6 +26,8 @@
>  #include "head.h"
>  #include "ior.h"
>
> +#include <drm/display/drm_dp.h>
> +
>  #include <subdev/bios.h>
>  #include <subdev/bios/init.h>
>  #include <subdev/gpio.h>
> @@ -634,6 +636,50 @@ nvkm_dp_enable_supported_link_rates(struct nvkm_outp
*outp)
>         return outp->dp.rates != 0;
>  }
>
> +/* XXX: This is a big fat hack, and this is just drm_dp_read_dpcd_caps()
Well.. maybe we should rephrase that _if_ we want to see it
backported. But is this code really that bad? It kinda looks
reasonable enough.
> + * converted to work inside nvkm. This is a temporary holdover until we
start
> + * passing the drm_dp_aux device through NVKM
> + */
> +static int
> +nvkm_dp_read_dpcd_caps(struct nvkm_outp *outp)
> +{
> +       struct nvkm_i2c_aux *aux = outp->dp.aux;
> +       u8 dpcd_ext[DP_RECEIVER_CAP_SIZE];
> +       int ret;
> +
> +       ret = nvkm_rdaux(aux, DPCD_RC00_DPCD_REV, outp->dp.dpcd,
DP_RECEIVER_CAP_SIZE);
> +       if (ret < 0)
> +               return ret;
> +
> +       /*
> +        * Prior to DP1.3 the bit represented by
> +        * DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT was reserved.
> +        * If it is set DP_DPCD_REV at 0000h could be at a value less than
> +        * the true capability of the panel. The only way to check is to
> +        * then compare 0000h and 2200h.
> +        */
> +       if (!(outp->dp.dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
> +             DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT))
> +               return 0;
> +
> +       ret = nvkm_rdaux(aux, DP_DP13_DPCD_REV, dpcd_ext,
sizeof(dpcd_ext));
> +       if (ret < 0)
> +               return ret;
> +
> +       if (outp->dp.dpcd[DP_DPCD_REV] > dpcd_ext[DP_DPCD_REV]) {
> +               OUTP_DBG(outp, "Extended DPCD rev less than base DPCD
rev (%d > %d)\n",
> +                        outp->dp.dpcd[DP_DPCD_REV],
dpcd_ext[DP_DPCD_REV]);
> +               return 0;
> +       }
> +
> +       if (!memcmp(outp->dp.dpcd, dpcd_ext, sizeof(dpcd_ext)))
> +               return 0;
> +
> +       memcpy(outp->dp.dpcd, dpcd_ext, sizeof(dpcd_ext));
> +
> +       return 0;
> +}
> +
>  void
>  nvkm_dp_enable(struct nvkm_outp *outp, bool auxpwr)
>  {
> @@ -689,7 +735,7 @@ nvkm_dp_enable(struct nvkm_outp *outp, bool auxpwr)
>                         memset(outp->dp.lttpr, 0x00,
sizeof(outp->dp.lttpr));
>                 }
>
> -               if (!nvkm_rdaux(aux, DPCD_RC00_DPCD_REV, outp->dp.dpcd,
sizeof(outp->dp.dpcd))) {
> +               if (!nvkm_dp_read_dpcd_caps(outp)) {
>                         const u8 rates[] = { 0x1e, 0x14, 0x0a, 0x06, 0 };
>                         const u8 *rate;
>                         int rate_max;
> --
> 2.40.1
>

On Sat, 8 Jul 2023 at 07:59, Lyude Paul <lyude at redhat.com>
wrote:
>
> Currently we use the drm_dp_dpcd_read_caps() helper in the DRM side of
> nouveau in order to read the DPCD of a DP connector, which makes sure we do
> the right thing and also check for extended DPCD caps. However, it turns
> out we're not currently doing this on the nvkm side since we don't
have
> access to the drm_dp_aux structure there - which means that the DRM side of
> the driver and the NVKM side can end up with different DPCD capabilities
> for the same connector.
>
> Ideally to fix this, we want to start setting up the drm_dp_aux device in
> NVKM before we've made contact with the DRM side - which should be
pretty
> easy to accomplish (I'm already working on it!). Until then however,
let's
> workaround this problem by porting a copy of drm_dp_read_dpcd_caps() into
> NVKM - which should fix this issue.
I wouldn't worry about this.  I'm moving basically everything to the
DRM side of the driver for the GSP work anyway.

Ben.
>
> Issue: https://gitlab.freedesktop.org/drm/nouveau/-/issues/211
> Signed-off-by: Lyude Paul <lyude at redhat.com>
> ---
>  drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c | 48 ++++++++++++++++++-
>  1 file changed, 47 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c
b/drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c
> index 40c8ea43c42f..b8ac66b4a2c4 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/engine/disp/dp.c
> @@ -26,6 +26,8 @@
>  #include "head.h"
>  #include "ior.h"
>
> +#include <drm/display/drm_dp.h>
> +
>  #include <subdev/bios.h>
>  #include <subdev/bios/init.h>
>  #include <subdev/gpio.h>
> @@ -634,6 +636,50 @@ nvkm_dp_enable_supported_link_rates(struct nvkm_outp
*outp)
>         return outp->dp.rates != 0;
>  }
>
> +/* XXX: This is a big fat hack, and this is just drm_dp_read_dpcd_caps()
> + * converted to work inside nvkm. This is a temporary holdover until we
start
> + * passing the drm_dp_aux device through NVKM
> + */
> +static int
> +nvkm_dp_read_dpcd_caps(struct nvkm_outp *outp)
> +{
> +       struct nvkm_i2c_aux *aux = outp->dp.aux;
> +       u8 dpcd_ext[DP_RECEIVER_CAP_SIZE];
> +       int ret;
> +
> +       ret = nvkm_rdaux(aux, DPCD_RC00_DPCD_REV, outp->dp.dpcd,
DP_RECEIVER_CAP_SIZE);
> +       if (ret < 0)
> +               return ret;
> +
> +       /*
> +        * Prior to DP1.3 the bit represented by
> +        * DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT was reserved.
> +        * If it is set DP_DPCD_REV at 0000h could be at a value less than
> +        * the true capability of the panel. The only way to check is to
> +        * then compare 0000h and 2200h.
> +        */
> +       if (!(outp->dp.dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
> +             DP_EXTENDED_RECEIVER_CAP_FIELD_PRESENT))
> +               return 0;
> +
> +       ret = nvkm_rdaux(aux, DP_DP13_DPCD_REV, dpcd_ext,
sizeof(dpcd_ext));
> +       if (ret < 0)
> +               return ret;
> +
> +       if (outp->dp.dpcd[DP_DPCD_REV] > dpcd_ext[DP_DPCD_REV]) {
> +               OUTP_DBG(outp, "Extended DPCD rev less than base DPCD
rev (%d > %d)\n",
> +                        outp->dp.dpcd[DP_DPCD_REV],
dpcd_ext[DP_DPCD_REV]);
> +               return 0;
> +       }
> +
> +       if (!memcmp(outp->dp.dpcd, dpcd_ext, sizeof(dpcd_ext)))
> +               return 0;
> +
> +       memcpy(outp->dp.dpcd, dpcd_ext, sizeof(dpcd_ext));
> +
> +       return 0;
> +}
> +
>  void
>  nvkm_dp_enable(struct nvkm_outp *outp, bool auxpwr)
>  {
> @@ -689,7 +735,7 @@ nvkm_dp_enable(struct nvkm_outp *outp, bool auxpwr)
>                         memset(outp->dp.lttpr, 0x00,
sizeof(outp->dp.lttpr));
>                 }
>
> -               if (!nvkm_rdaux(aux, DPCD_RC00_DPCD_REV, outp->dp.dpcd,
sizeof(outp->dp.dpcd))) {
> +               if (!nvkm_dp_read_dpcd_caps(outp)) {
>                         const u8 rates[] = { 0x1e, 0x14, 0x0a, 0x06, 0 };
>                         const u8 *rate;
>                         int rate_max;
> --
> 2.40.1
>