Nouveau - Sep 2020 - [PATCH v2 1/2] drm/nouveau/kms/nv50-: Get rid of bogus nouveau_conn_mode_valid()

Ville also pointed out that I got a lot of the logic here wrong as well, whoops.
While I don't think anyone's likely using 3D output with nouveau, the
next patch
will make nouveau_conn_mode_valid() make a lot less sense. So, let's just
get
rid of it and open-code it like before, while taking care to move the 3D frame
packing calculations on the dot clock into the right place.

Signed-off-by: Lyude Paul <lyude at redhat.com>
Fixes: d6a9efece724 ("drm/nouveau/kms/nv50-: Share DP SST mode_valid()
handling with MST")
Cc: Ville Syrj?l? <ville.syrjala at linux.intel.com>
Cc: <stable at vger.kernel.org> # v5.8+
---
 drivers/gpu/drm/nouveau/nouveau_connector.c | 36 ++++++---------------
 drivers/gpu/drm/nouveau/nouveau_dp.c        | 16 ++++++---
 2 files changed, 21 insertions(+), 31 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_connector.c
b/drivers/gpu/drm/nouveau/nouveau_connector.c
index 49dd0cbc332f..6f21f36719fc 100644
--- a/drivers/gpu/drm/nouveau/nouveau_connector.c
+++ b/drivers/gpu/drm/nouveau/nouveau_connector.c
@@ -1023,29 +1023,6 @@ get_tmds_link_bandwidth(struct drm_connector *connector)
 		return 112000 * duallink_scale;
 }
 
-enum drm_mode_status
-nouveau_conn_mode_clock_valid(const struct drm_display_mode *mode,
-			      const unsigned min_clock,
-			      const unsigned max_clock,
-			      unsigned int *clock_out)
-{
-	unsigned int clock = mode->clock;
-
-	if ((mode->flags & DRM_MODE_FLAG_3D_MASK) =-	   
DRM_MODE_FLAG_3D_FRAME_PACKING)
-		clock *= 2;
-
-	if (clock < min_clock)
-		return MODE_CLOCK_LOW;
-	if (clock > max_clock)
-		return MODE_CLOCK_HIGH;
-
-	if (clock_out)
-		*clock_out = clock;
-
-	return MODE_OK;
-}
-
 static enum drm_mode_status
 nouveau_connector_mode_valid(struct drm_connector *connector,
 			     struct drm_display_mode *mode)
@@ -1053,7 +1030,7 @@ nouveau_connector_mode_valid(struct drm_connector
*connector,
 	struct nouveau_connector *nv_connector = nouveau_connector(connector);
 	struct nouveau_encoder *nv_encoder = nv_connector->detected_encoder;
 	struct drm_encoder *encoder = to_drm_encoder(nv_encoder);
-	unsigned min_clock = 25000, max_clock = min_clock;
+	unsigned int min_clock = 25000, max_clock = min_clock, clock = mode->clock;
 
 	switch (nv_encoder->dcb->type) {
 	case DCB_OUTPUT_LVDS:
@@ -1082,8 +1059,15 @@ nouveau_connector_mode_valid(struct drm_connector
*connector,
 		return MODE_BAD;
 	}
 
-	return nouveau_conn_mode_clock_valid(mode, min_clock, max_clock,
-					     NULL);
+	if ((mode->flags & DRM_MODE_FLAG_3D_MASK) ==
DRM_MODE_FLAG_3D_FRAME_PACKING)
+		clock *= 2;
+
+	if (clock < min_clock)
+		return MODE_CLOCK_LOW;
+	if (clock > max_clock)
+		return MODE_CLOCK_HIGH;
+
+	return MODE_OK;
 }
 
 static struct drm_encoder *
diff --git a/drivers/gpu/drm/nouveau/nouveau_dp.c
b/drivers/gpu/drm/nouveau/nouveau_dp.c
index 7b640e05bd4c..93e3751ad7f1 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dp.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dp.c
@@ -232,12 +232,14 @@ nv50_dp_mode_valid(struct drm_connector *connector,
 		   unsigned *out_clock)
 {
 	const unsigned min_clock = 25000;
-	unsigned max_clock, ds_clock, clock;
-	enum drm_mode_status ret;
+	unsigned max_clock, ds_clock, clock = mode->clock;
 
 	if (mode->flags & DRM_MODE_FLAG_INTERLACE &&
!outp->caps.dp_interlace)
 		return MODE_NO_INTERLACE;
 
+	if ((mode->flags & DRM_MODE_FLAG_3D_MASK) ==
DRM_MODE_FLAG_3D_FRAME_PACKING)
+		clock *= 2;
+
 	max_clock = outp->dp.link_nr * outp->dp.link_bw;
 	ds_clock = drm_dp_downstream_max_dotclock(outp->dp.dpcd,
 						  outp->dp.downstream_ports);
@@ -245,9 +247,13 @@ nv50_dp_mode_valid(struct drm_connector *connector,
 		max_clock = min(max_clock, ds_clock);
 
 	clock = mode->clock * (connector->display_info.bpc * 3) / 10;
-	ret = nouveau_conn_mode_clock_valid(mode, min_clock, max_clock,
-					    &clock);
+	if (clock < min_clock)
+		return MODE_CLOCK_LOW;
+	if (clock > max_clock)
+		return MODE_CLOCK_HIGH;
+
 	if (out_clock)
 		*out_clock = clock;
-	return ret;
+
+	return MODE_OK;
 }
-- 
2.26.2

While I thought I had this correct (since it actually did reject modes
like I expected during testing), Ville Syrjala from Intel pointed out
that the logic here isn't correct. max_clock refers to the max data rate
supported by the DP encoder. So, limiting it to the output of ds_clock (which
refers to the maximum dotclock of the downstream DP device) doesn't make any
sense. Additionally, since we're using the connector's bpc as the
canonical BPC
we should use this in mode_valid until we support dynamically setting the bpp
based on bandwidth constraints.

https://lists.freedesktop.org/archives/dri-devel/2020-September/280276.html

For more info.

So, let's rewrite this using Ville's advice.

v2:
* Ville pointed out I mixed up the dotclock and the link rate. So fix that...
* ...and also rename all the variables in this function to be more appropriately
  labeled so I stop mixing them up.
* Reuse the bpp from the connector for now until we have dynamic bpp selection.
* Use use DIV_ROUND_UP for calculating the mode rate like i915 does, which we
  should also have been doing from the start

Signed-off-by: Lyude Paul <lyude at redhat.com>
Fixes: 409d38139b42 ("drm/nouveau/kms/nv50-: Use downstream DP clock limits
for mode validation")
Cc: Ville Syrj?l? <ville.syrjala at linux.intel.com>
Cc: Lyude Paul <lyude at redhat.com>
Cc: Ben Skeggs <bskeggs at redhat.com>
---
 drivers/gpu/drm/nouveau/nouveau_dp.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_dp.c
b/drivers/gpu/drm/nouveau/nouveau_dp.c
index 93e3751ad7f1..040ed88d362d 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dp.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dp.c
@@ -231,8 +231,9 @@ nv50_dp_mode_valid(struct drm_connector *connector,
 		   const struct drm_display_mode *mode,
 		   unsigned *out_clock)
 {
-	const unsigned min_clock = 25000;
-	unsigned max_clock, ds_clock, clock = mode->clock;
+	const unsigned int min_clock = 25000;
+	unsigned int max_rate, mode_rate, ds_max_dotclock, clock = mode->clock;
+	const u8 bpp = connector->display_info.bpc * 3;
 
 	if (mode->flags & DRM_MODE_FLAG_INTERLACE &&
!outp->caps.dp_interlace)
 		return MODE_NO_INTERLACE;
@@ -240,17 +241,17 @@ nv50_dp_mode_valid(struct drm_connector *connector,
 	if ((mode->flags & DRM_MODE_FLAG_3D_MASK) ==
DRM_MODE_FLAG_3D_FRAME_PACKING)
 		clock *= 2;
 
-	max_clock = outp->dp.link_nr * outp->dp.link_bw;
-	ds_clock = drm_dp_downstream_max_dotclock(outp->dp.dpcd,
-						  outp->dp.downstream_ports);
-	if (ds_clock)
-		max_clock = min(max_clock, ds_clock);
+	max_rate = outp->dp.link_nr * outp->dp.link_bw;
+	mode_rate = DIV_ROUND_UP(clock * bpp, 8);
+	if (mode_rate > max_rate)
+		return MODE_CLOCK_HIGH;
+
+	ds_max_dotclock = drm_dp_downstream_max_dotclock(outp->dp.dpcd,
outp->dp.downstream_ports);
+	if (ds_max_dotclock && clock > ds_max_dotclock)
+		return MODE_CLOCK_HIGH;
 
-	clock = mode->clock * (connector->display_info.bpc * 3) / 10;
 	if (clock < min_clock)
 		return MODE_CLOCK_LOW;
-	if (clock > max_clock)
-		return MODE_CLOCK_HIGH;
 
 	if (out_clock)
 		*out_clock = clock;
-- 
2.26.2