linux-kernel - [PATCH v5 06/19] drm/connector: hdmi: Use YUV420 output format as an RGB fallback

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Message-Id: <20250527-hdmi-conn-yuv-v5-6-74c9c4a8ac0c@collabora.com>
Date: Tue, 27 May 2025 15:11:14 +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 v5 06/19] 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 | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/display/drm_hdmi_state_helper.c b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
index a9733a2e1b632e02f535c5ece64762f8ed9e4af2..2c641add743466841cb2e777a07633dc5686ccd8 100644
--- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
+++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
@@ -649,12 +649,22 @@ 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) {
+		if (connector->ycbcr_420_allowed) {
+			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");
+		} else {
+			drm_dbg_kms(connector->dev,
+				    "YUV420 output format not allowed for connector.\n");
+			ret = -EINVAL;
+		}
+	}
 
 	return ret;
 }

-- 
2.49.0