[PATCH v2] drm: Guard DRM_CLIENT_CAP_PLANE_COLOR_PIPELINE

[Robert Mader <robert.mader@collabora.com>]

The client cap is currently advertised unconditionally, even for drivers
that do not support plane color pipelines. If clients supporting the later,
like Wayland compositors or tools like drm_info, enable the client cap on
such drivers they will be left without both color pipeline and the legacy
properties COLOR_ENCODING and COLOR_RANGE, effectively breaking YUV->RGB
conversion support.

Prevent that by only marking the cap supported if there are actually planes
with color pipelines.

Note: while the color pipeline replacement for the legacy properties is
still under review (1), we can assume that it will work as a drop-in
replacement. That means any plane on any hardware currently supporting
the legacy properties will be able to offer a functionally equal color
pipeline and there will be no technical reason keep using the legacy
properties if both the driver and the client support the new API.

1: https://lore.kernel.org/dri-devel/20260623164812.81110-1-harry.wentland@amd.com/

Signed-off-by: Robert Mader <robert.mader@collabora.com>

---

Changes in v2:
 - Replace the driver feature with a simple check (suggested by Maarten
   Lankhorst <maarten.lankhorst@linux.intel.com>)
 - Expand the commit message slightly and change the title
---
 drivers/gpu/drm/drm_ioctl.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index e2df4becce62..b2c0234eaf14 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -373,13 +373,26 @@ drm_setclientcap(struct drm_device *dev, void *data, struct drm_file *file_priv)
 			return -EINVAL;
 		file_priv->supports_virtualized_cursor_plane = req->value;
 		break;
-	case DRM_CLIENT_CAP_PLANE_COLOR_PIPELINE:
+	case DRM_CLIENT_CAP_PLANE_COLOR_PIPELINE: {
+		struct drm_plane *plane;
+		bool has_plane_with_color_pipeline = false;
+
+		drm_for_each_plane(plane, dev) {
+			if (plane->color_pipeline_property) {
+				has_plane_with_color_pipeline = true;
+				break;
+			}
+		}
+		if (!has_plane_with_color_pipeline)
+			return -EOPNOTSUPP;
+
 		if (!file_priv->atomic)
 			return -EINVAL;
 		if (req->value > 1)
 			return -EINVAL;
 		file_priv->plane_color_pipeline = req->value;
 		break;
+	}
 	default:
 		return -EINVAL;
 	}
-- 
2.55.0