linux-kernel - [PATCH v4 06/23] drm/connector: hdmi: Use YUV420 output format as an RGB fallback

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Message-Id: <20250425-hdmi-conn-yuv-v4-6-5e55e2aaa3fa@collabora.com>
Date: Fri, 25 Apr 2025 13:26:57 +0300
From: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Dave Stevenson <dave.stevenson@...pberrypi.com>, 
 Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>, 
 Dmitry Baryshkov <lumag@...nel.org>, Dmitry Baryshkov <lumag@...nel.org>
Cc: kernel@...labora.com, dri-devel@...ts.freedesktop.org, 
 linux-kernel@...r.kernel.org
Subject: [PATCH v4 06/23] drm/connector: hdmi: Use YUV420 output format as
 an RGB fallback

Try to make use of YUV420 when computing the best output format and
RGB cannot be supported for any of the available color depths.

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
---
 drivers/gpu/drm/display/drm_hdmi_state_helper.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/display/drm_hdmi_state_helper.c b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
index 9e0a468073acbb2477eff1abef1c09d63620afaa..1fba10b92a6baa49150b6ff1e96bf2c2739bf269 100644
--- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
+++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
@@ -648,14 +648,26 @@ hdmi_compute_config(const struct drm_connector *connector,
 				       8, connector->max_bpc);
 	int ret;
 
-	/*
-	 * TODO: Add support for YCbCr420 output for HDMI 2.0 capable
-	 * devices, for modes that only support YCbCr420.
-	 */
 	ret = hdmi_compute_format_bpc(connector, conn_state, mode, max_bpc,
 				      HDMI_COLORSPACE_RGB);
+	if (!ret)
+		return 0;
 
-	return ret;
+	if (!connector->ycbcr_420_allowed) {
+		drm_dbg_kms(connector->dev,
+			    "YUV420 output format not allowed for connector.\n");
+		return -EINVAL;
+	}
+
+	ret = hdmi_compute_format_bpc(connector, conn_state, mode, max_bpc,
+				      HDMI_COLORSPACE_YUV420);
+	if (ret) {
+		drm_dbg_kms(connector->dev,
+			    "YUV420 output format doesn't work.\n");
+		return ret;
+	}
+
+	return 0;
 }
 
 static int hdmi_generate_avi_infoframe(const struct drm_connector *connector,

-- 
2.49.0