[PATCH v7 0/3] drm/i915/display: Try YCbCr420 color when RGB fails

[PATCH v7 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 7. Fixed a rebase issue in 1/3 and moved message
from error output to debug output in 2/3.

[PATCH v7 1/3] drm/i915/display: New function to avoid duplicate code in upcomming commits

[Werner Sembach]

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

Signed-off-by: Werner Sembach <wse@tuxedocomputers.com>
---
 drivers/gpu/drm/i915/display/intel_hdmi.c | 42 +++++++++++++++--------
 1 file changed, 27 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..2f1ca91387e4 100644
--- a/drivers/gpu/drm/i915/display/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
@@ -1861,6 +1861,32 @@ 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, 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);
+	}
+
+	return status;
+}
+
 static enum drm_mode_status
 intel_hdmi_mode_valid(struct drm_connector *connector,
 		      struct drm_display_mode *mode)
@@ -1891,21 +1917,7 @@ 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 v7 2/3] drm/i915/display: 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.

A slight change in behaviour occurs with this patch: 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>
---
 drivers/gpu/drm/i915/display/intel_hdmi.c | 66 ++++++++++++-----------
 1 file changed, 35 insertions(+), 31 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
index 2f1ca91387e4..c411f1862286 100644
--- a/drivers/gpu/drm/i915/display/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
@@ -2000,29 +2000,6 @@ 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)
@@ -2129,6 +2106,31 @@ 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_dbg_kms(&i915->drm,
+				    "YCbCr 4:2:0 mode but YCbCr 4:2:0 output not possible. Falling back to RGB.\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)
@@ -2153,23 +2155,25 @@ 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 v7 3/3] drm/i915/display: 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>
---
 drivers/gpu/drm/i915/display/intel_hdmi.c | 25 ++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
index c411f1862286..6e135662da3e 100644
--- a/drivers/gpu/drm/i915/display/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
@@ -1898,6 +1898,7 @@ 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;
@@ -1914,12 +1915,22 @@ 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);
 }
@@ -2127,6 +2138,14 @@ 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

Re: [PATCH v7 0/3] drm/i915/display: Try YCbCr420 color when RGB fails

[Ville Syrjälä]

On Mon, May 10, 2021 at 03:33:46PM +0200, Werner Sembach wrote:
> 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 7. Fixed a rebase issue in 1/3 and moved message
> from error output to debug output in 2/3.

Looks good and CI seem shappy. 

Series pushed to drm-intel-next. Thanks.

-- 
Ville Syrjälä
Intel