[PATCH 0/3] drm/i915/display Try YCbCr420 color when RGB fails

[PATCH 0/3] drm/i915/display Try YCbCr420 color when RGB fails

[Werner Sembach]

When encoder validation of a display mode fails, retry with less bandwidth
heavy YCbCr420 color mode, if available. This enables some HDMI 1.4 setups
to support 4k60Hz output, which previously failed silently.

AMDGPU had nearly the exact same issue. This problem description is
therefore copied from my commit message of the AMDGPU patch.

On some setups, while the monitor and the gpu support display modes with
pixel clocks of up to 600MHz, the link encoder might not. This prevents
YCbCr444 and RGB encoding for 4k60Hz, but YCbCr420 encoding might still be
possible. However, which color mode is used is decided before the link
encoder capabilities are checked. This patch fixes the problem by retrying
to find a display mode with YCbCr420 enforced and using it, if it is
valid.

This patchset is revision 4. After getting clarification on questions ask
on the mailing list.

[PATCH 1/3] New function to avoid duplicate code in upcomming commits

[Werner Sembach]

Moves some checks that later will be performed 2 times to an own fuction. This
avoids duplicate code later on.

Signed-off-by: Werner Sembach <wse@tuxedocomputers.com>
---

From 42a4a3a7d9ea9948b4071f406e7fcae23bfa0bdf Mon Sep 17 00:00:00 2001
From: Werner Sembach <wse@tuxedocomputers.com>
Date: Mon, 3 May 2021 14:35:39 +0200
Subject: [PATCH 1/3] New function to avoid duplicate code in upcomming commits

---
 drivers/gpu/drm/i915/display/intel_hdmi.c | 41 ++++++++++++++---------
 1 file changed, 26 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
index 46de56af33db..576d3d910d06 100644
--- a/drivers/gpu/drm/i915/display/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
@@ -1861,6 +1861,31 @@ static int intel_hdmi_port_clock(int clock, int bpc)
 	return clock * bpc / 8;
 }
 
+static enum drm_mode_status
+intel_hdmi_mode_clock_valid(struct intel_hdmi *hdmi, int clock, bool has_hdmi_sink)
+{
+	struct drm_device *dev = intel_hdmi_to_dev(hdmi);
+	struct drm_i915_private *dev_priv = to_i915(dev);
+	enum drm_mode_status status;
+
+	/* check if we can do 8bpc */
+	status = hdmi_port_clock_valid(hdmi, clock, true, has_hdmi_sink);
+
+	if (has_hdmi_sink) {
+		/* if we can't do 8bpc we may still be able to do 12bpc */
+		if (status != MODE_OK && !HAS_GMCH(dev_priv))
+			status = hdmi_port_clock_valid(hdmi, clock * 3 / 2,
+						       true, has_hdmi_sink);
+
+		/* if we can't do 8,12bpc we may still be able to do 10bpc */
+		if (status != MODE_OK && INTEL_GEN(dev_priv) >= 11)
+			status = hdmi_port_clock_valid(hdmi, clock * 5 / 4,
+						       true, has_hdmi_sink);
+	}
+
+	return status;
+}
+
 static enum drm_mode_status
 intel_hdmi_mode_valid(struct drm_connector *connector,
 		      struct drm_display_mode *mode)
@@ -1891,21 +1916,7 @@ intel_hdmi_mode_valid(struct drm_connector *connector,
 	if (drm_mode_is_420_only(&connector->display_info, mode))
 		clock /= 2;
 
-	/* check if we can do 8bpc */
-	status = hdmi_port_clock_valid(hdmi, intel_hdmi_port_clock(clock, 8),
-				       true, has_hdmi_sink);
-
-	if (has_hdmi_sink) {
-		/* if we can't do 8bpc we may still be able to do 12bpc */
-		if (status != MODE_OK && !HAS_GMCH(dev_priv))
-			status = hdmi_port_clock_valid(hdmi, intel_hdmi_port_clock(clock, 12),
-						       true, has_hdmi_sink);
-
-		/* if we can't do 8,12bpc we may still be able to do 10bpc */
-		if (status != MODE_OK && DISPLAY_VER(dev_priv) >= 11)
-			status = hdmi_port_clock_valid(hdmi, intel_hdmi_port_clock(clock, 10),
-						       true, has_hdmi_sink);
-	}
+	status = intel_hdmi_mode_clock_valid(hdmi, clock, has_hdmi_sink);
 	if (status != MODE_OK)
 		return status;
 
-- 
2.25.1

[PATCH 2/3] Restructure output format computation for better expandability

[Werner Sembach]

Couples the decission between RGB and YCbCr420 mode and the check if the port
clock can archive the required frequency. Other checks and configuration steps
that where previously done in between can also be done before or after.

This allows for are cleaner implementation of retrying different color
encodings.

Slight change in behaviour: If YCbCr420 is not allowed but display is YCbCr420
only it no longer fails, but just prints an error and tries to fallback on RGB.

Signed-off-by: Werner Sembach <wse@tuxedocomputers.com>
---
Imho an error message in when YCbCR420 not allowed meets YCbCr420 only can be
a usefull bugfinding tool for cases of blackscreen on exotic configurations.

I'm unsure if this should be a warning instead.

From 883678ef703b6bb15cd2883eb2c5ce27d07911d3 Mon Sep 17 00:00:00 2001
From: Werner Sembach <wse@tuxedocomputers.com>
Date: Mon, 3 May 2021 15:30:40 +0200
Subject: [PATCH 2/3] Restructure output format computation for better
 expandability

---
 drivers/gpu/drm/i915/display/intel_hdmi.c | 65 ++++++++++++-----------
 1 file changed, 34 insertions(+), 31 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
index 576d3d910d06..b0201d4f27eb 100644
--- a/drivers/gpu/drm/i915/display/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
@@ -1999,29 +1999,6 @@ static bool hdmi_deep_color_possible(const struct intel_crtc_state *crtc_state,
 					      INTEL_OUTPUT_FORMAT_YCBCR420);
 }
 
-static int
-intel_hdmi_ycbcr420_config(struct intel_crtc_state *crtc_state,
-			   const struct drm_connector_state *conn_state)
-{
-	struct drm_connector *connector = conn_state->connector;
-	struct drm_i915_private *i915 = to_i915(connector->dev);
-	const struct drm_display_mode *adjusted_mode =
-		&crtc_state->hw.adjusted_mode;
-
-	if (!drm_mode_is_420_only(&connector->display_info, adjusted_mode))
-		return 0;
-
-	if (!connector->ycbcr_420_allowed) {
-		drm_err(&i915->drm,
-			"Platform doesn't support YCBCR420 output\n");
-		return -EINVAL;
-	}
-
-	crtc_state->output_format = INTEL_OUTPUT_FORMAT_YCBCR420;
-
-	return intel_pch_panel_fitting(crtc_state, conn_state);
-}
-
 static int intel_hdmi_compute_bpc(struct intel_encoder *encoder,
 				  struct intel_crtc_state *crtc_state,
 				  int clock)
@@ -2128,6 +2105,30 @@ static bool intel_hdmi_has_audio(struct intel_encoder *encoder,
 		return intel_conn_state->force_audio == HDMI_AUDIO_ON;
 }
 
+static int intel_hdmi_compute_output_format(struct intel_encoder *encoder,
+				     struct intel_crtc_state *crtc_state,
+				     const struct drm_connector_state *conn_state)
+{
+	struct drm_connector *connector = conn_state->connector;
+	struct drm_i915_private *i915 = to_i915(connector->dev);
+	const struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
+	int ret;
+	bool ycbcr_420_only;
+
+	ycbcr_420_only = drm_mode_is_420_only(&connector->display_info, adjusted_mode);
+	if (connector->ycbcr_420_allowed && ycbcr_420_only)
+		crtc_state->output_format = INTEL_OUTPUT_FORMAT_YCBCR420;
+	else {
+		if (!connector->ycbcr_420_allowed && ycbcr_420_only)
+			drm_err(&i915->drm, "Display only supports YCbCr420 output, but connector does not allow it. Fallback to RGB, but this will likely fail.\n");
+		crtc_state->output_format = INTEL_OUTPUT_FORMAT_RGB;
+	}
+
+	ret = intel_hdmi_compute_clock(encoder, crtc_state);
+
+	return ret;
+}
+
 int intel_hdmi_compute_config(struct intel_encoder *encoder,
 			      struct intel_crtc_state *pipe_config,
 			      struct drm_connector_state *conn_state)
@@ -2152,23 +2153,25 @@ int intel_hdmi_compute_config(struct intel_encoder *encoder,
 	if (adjusted_mode->flags & DRM_MODE_FLAG_DBLCLK)
 		pipe_config->pixel_multiplier = 2;
 
-	ret = intel_hdmi_ycbcr420_config(pipe_config, conn_state);
-	if (ret)
-		return ret;
-
-	pipe_config->limited_color_range =
-		intel_hdmi_limited_color_range(pipe_config, conn_state);
-
 	if (HAS_PCH_SPLIT(dev_priv) && !HAS_DDI(dev_priv))
 		pipe_config->has_pch_encoder = true;
 
 	pipe_config->has_audio =
 		intel_hdmi_has_audio(encoder, pipe_config, conn_state);
 
-	ret = intel_hdmi_compute_clock(encoder, pipe_config);
+	ret = intel_hdmi_compute_output_format(encoder, pipe_config, conn_state);
 	if (ret)
 		return ret;
 
+	if (pipe_config->output_format == INTEL_OUTPUT_FORMAT_YCBCR420) {
+		ret = intel_pch_panel_fitting(pipe_config, conn_state);
+		if (ret)
+			return ret;
+	}
+
+	pipe_config->limited_color_range =
+		intel_hdmi_limited_color_range(pipe_config, conn_state);
+
 	if (conn_state->picture_aspect_ratio)
 		adjusted_mode->picture_aspect_ratio =
 			conn_state->picture_aspect_ratio;
-- 
2.25.1

[PATCH 3/3] Use YCbCr420 as fallback when RGB fails

[Werner Sembach]

When encoder validation of a display mode fails, retry with less bandwidth
heavy YCbCr420 color mode, if available. This enables some HDMI 1.4 setups
to support 4k60Hz output, which previously failed silently.

AMDGPU had nearly the exact same issue. This problem description is
therefore copied from my commit message of the AMDGPU patch.

On some setups, while the monitor and the gpu support display modes with
pixel clocks of up to 600MHz, the link encoder might not. This prevents
YCbCr444 and RGB encoding for 4k60Hz, but YCbCr420 encoding might still be
possible. However, which color mode is used is decided before the link
encoder capabilities are checked. This patch fixes the problem by retrying
to find a display mode with YCbCr420 enforced and using it, if it is
valid.

Signed-off-by: Werner Sembach <wse@tuxedocomputers.com>
---
Now with the suggestes change as it does makes a difference ^^

From dc2fb79273f2c75a08b76bf912949ff3e433056b Mon Sep 17 00:00:00 2001
From: Werner Sembach <wse@tuxedocomputers.com>
Date: Mon, 3 May 2021 16:23:17 +0200
Subject: [PATCH 3/3] Use YCbCr420 as fallback when RGB fails

---
 drivers/gpu/drm/i915/display/intel_hdmi.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
index b0201d4f27eb..5af6aef0acbf 100644
--- a/drivers/gpu/drm/i915/display/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
@@ -1897,6 +1897,7 @@ intel_hdmi_mode_valid(struct drm_connector *connector,
 	int clock = mode->clock;
 	int max_dotclk = to_i915(connector->dev)->max_dotclk_freq;
 	bool has_hdmi_sink = intel_has_hdmi_sink(hdmi, connector->state);
+    bool ycbcr_420_only;
 
 	if (mode->flags & DRM_MODE_FLAG_DBLSCAN)
 		return MODE_NO_DBLESCAN;
@@ -1913,12 +1914,20 @@ intel_hdmi_mode_valid(struct drm_connector *connector,
 		clock *= 2;
 	}
 
-	if (drm_mode_is_420_only(&connector->display_info, mode))
+	ycbcr_420_only = drm_mode_is_420_only(&connector->display_info, mode);
+	if (ycbcr_420_only)
 		clock /= 2;
 
 	status = intel_hdmi_mode_clock_valid(hdmi, clock, has_hdmi_sink);
-	if (status != MODE_OK)
-		return status;
+	if (status != MODE_OK) {
+		if (ycbcr_420_only || !connector->ycbcr_420_allowed || !drm_mode_is_420_also(&connector->display_info, mode))
+			return status;
+
+		clock /= 2;
+		status = intel_hdmi_mode_clock_valid(hdmi, clock, has_hdmi_sink);
+		if (status != MODE_OK)
+			return status;
+	}
 
 	return intel_mode_valid_max_plane_size(dev_priv, mode, false);
 }
@@ -2125,6 +2134,14 @@ static int intel_hdmi_compute_output_format(struct intel_encoder *encoder,
 	}
 
 	ret = intel_hdmi_compute_clock(encoder, crtc_state);
+	if (ret) {
+		if (crtc_state->output_format != INTEL_OUTPUT_FORMAT_YCBCR420 &&
+				connector->ycbcr_420_allowed &&
+				drm_mode_is_420_also(&connector->display_info, adjusted_mode)) {
+			crtc_state->output_format = INTEL_OUTPUT_FORMAT_YCBCR420;
+			ret = intel_hdmi_compute_clock(encoder, crtc_state);
+		}
+	}
 
 	return ret;
 }
-- 
2.25.1

[PATCH 1/3] New function to avoid duplicate code in upcomming commits

[Werner Sembach]

Moves some checks that later will be performed 2 times to an own fuction. This
avoids duplicate code later on.

Signed-off-by: Werner Sembach <wse@tuxedocomputers.com>
---

From 42a4a3a7d9ea9948b4071f406e7fcae23bfa0bdf Mon Sep 17 00:00:00 2001
From: Werner Sembach <wse@tuxedocomputers.com>
Date: Mon, 3 May 2021 14:35:39 +0200
Subject: [PATCH 1/3] New function to avoid duplicate code in upcomming commits

---
 drivers/gpu/drm/i915/display/intel_hdmi.c | 41 ++++++++++++++---------
 1 file changed, 26 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
index 46de56af33db..576d3d910d06 100644
--- a/drivers/gpu/drm/i915/display/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
@@ -1861,6 +1861,31 @@ static int intel_hdmi_port_clock(int clock, int bpc)
 	return clock * bpc / 8;
 }
 
+static enum drm_mode_status
+intel_hdmi_mode_clock_valid(struct intel_hdmi *hdmi, int clock, bool has_hdmi_sink)
+{
+	struct drm_device *dev = intel_hdmi_to_dev(hdmi);
+	struct drm_i915_private *dev_priv = to_i915(dev);
+	enum drm_mode_status status;
+
+	/* check if we can do 8bpc */
+	status = hdmi_port_clock_valid(hdmi, clock, true, has_hdmi_sink);
+
+	if (has_hdmi_sink) {
+		/* if we can't do 8bpc we may still be able to do 12bpc */
+		if (status != MODE_OK && !HAS_GMCH(dev_priv))
+			status = hdmi_port_clock_valid(hdmi, clock * 3 / 2,
+						       true, has_hdmi_sink);
+
+		/* if we can't do 8,12bpc we may still be able to do 10bpc */
+		if (status != MODE_OK && INTEL_GEN(dev_priv) >= 11)
+			status = hdmi_port_clock_valid(hdmi, clock * 5 / 4,
+						       true, has_hdmi_sink);
+	}
+
+	return status;
+}
+
 static enum drm_mode_status
 intel_hdmi_mode_valid(struct drm_connector *connector,
 		      struct drm_display_mode *mode)
@@ -1891,21 +1916,7 @@ intel_hdmi_mode_valid(struct drm_connector *connector,
 	if (drm_mode_is_420_only(&connector->display_info, mode))
 		clock /= 2;
 
-	/* check if we can do 8bpc */
-	status = hdmi_port_clock_valid(hdmi, intel_hdmi_port_clock(clock, 8),
-				       true, has_hdmi_sink);
-
-	if (has_hdmi_sink) {
-		/* if we can't do 8bpc we may still be able to do 12bpc */
-		if (status != MODE_OK && !HAS_GMCH(dev_priv))
-			status = hdmi_port_clock_valid(hdmi, intel_hdmi_port_clock(clock, 12),
-						       true, has_hdmi_sink);
-
-		/* if we can't do 8,12bpc we may still be able to do 10bpc */
-		if (status != MODE_OK && DISPLAY_VER(dev_priv) >= 11)
-			status = hdmi_port_clock_valid(hdmi, intel_hdmi_port_clock(clock, 10),
-						       true, has_hdmi_sink);
-	}
+	status = intel_hdmi_mode_clock_valid(hdmi, clock, has_hdmi_sink);
 	if (status != MODE_OK)
 		return status;
 
-- 
2.25.1

[PATCH 1/3] New function to avoid duplicate code in upcomming commits

[Werner Sembach]

Moves some checks that later will be performed 2 times to an own fuction. This
avoids duplicate code later on.

Signed-off-by: Werner Sembach <wse@tuxedocomputers.com>
---
PS.: I have no idea why git send-email is messing up this timestamp in "From" below.

From 42a4a3a7d9ea9948b4071f406e7fcae23bfa0bdf Mon Sep 17 00:00:00 2001
From: Werner Sembach <wse@tuxedocomputers.com>
Date: Mon, 3 May 2021 14:35:39 +0200
Subject: [PATCH 1/3] New function to avoid duplicate code in upcomming commits

---
 drivers/gpu/drm/i915/display/intel_hdmi.c | 41 ++++++++++++++---------
 1 file changed, 26 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
index 46de56af33db..576d3d910d06 100644
--- a/drivers/gpu/drm/i915/display/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
@@ -1861,6 +1861,31 @@ static int intel_hdmi_port_clock(int clock, int bpc)
 	return clock * bpc / 8;
 }
 
+static enum drm_mode_status
+intel_hdmi_mode_clock_valid(struct intel_hdmi *hdmi, int clock, bool has_hdmi_sink)
+{
+	struct drm_device *dev = intel_hdmi_to_dev(hdmi);
+	struct drm_i915_private *dev_priv = to_i915(dev);
+	enum drm_mode_status status;
+
+	/* check if we can do 8bpc */
+	status = hdmi_port_clock_valid(hdmi, clock, true, has_hdmi_sink);
+
+	if (has_hdmi_sink) {
+		/* if we can't do 8bpc we may still be able to do 12bpc */
+		if (status != MODE_OK && !HAS_GMCH(dev_priv))
+			status = hdmi_port_clock_valid(hdmi, clock * 3 / 2,
+						       true, has_hdmi_sink);
+
+		/* if we can't do 8,12bpc we may still be able to do 10bpc */
+		if (status != MODE_OK && INTEL_GEN(dev_priv) >= 11)
+			status = hdmi_port_clock_valid(hdmi, clock * 5 / 4,
+						       true, has_hdmi_sink);
+	}
+
+	return status;
+}
+
 static enum drm_mode_status
 intel_hdmi_mode_valid(struct drm_connector *connector,
 		      struct drm_display_mode *mode)
@@ -1891,21 +1916,7 @@ intel_hdmi_mode_valid(struct drm_connector *connector,
 	if (drm_mode_is_420_only(&connector->display_info, mode))
 		clock /= 2;
 
-	/* check if we can do 8bpc */
-	status = hdmi_port_clock_valid(hdmi, intel_hdmi_port_clock(clock, 8),
-				       true, has_hdmi_sink);
-
-	if (has_hdmi_sink) {
-		/* if we can't do 8bpc we may still be able to do 12bpc */
-		if (status != MODE_OK && !HAS_GMCH(dev_priv))
-			status = hdmi_port_clock_valid(hdmi, intel_hdmi_port_clock(clock, 12),
-						       true, has_hdmi_sink);
-
-		/* if we can't do 8,12bpc we may still be able to do 10bpc */
-		if (status != MODE_OK && DISPLAY_VER(dev_priv) >= 11)
-			status = hdmi_port_clock_valid(hdmi, intel_hdmi_port_clock(clock, 10),
-						       true, has_hdmi_sink);
-	}
+	status = intel_hdmi_mode_clock_valid(hdmi, clock, has_hdmi_sink);
 	if (status != MODE_OK)
 		return status;
 
-- 
2.25.1