[PATCH] drm/amd/display: Reject YUV422 encoding over DP on DCE

["Timur Kristóf" <timur.kristof@gmail.com>]

Mark YUV422 unsupported over DP on DCE to work around a
regression caused by the recent YUV422 fallback patch.

See https://gitlab.freedesktop.org/drm/amd/-/issues/4585

The recent YUV422 fallback breaks DisplayPort on DCE6-10 because
it can select a high refresh rate mode with YUV422 and 6 BPC,
which is apparently not actually supported by the HW, causing
it to boot to a "no signal" screen.

Tested with a Samsung Odyssey G7 on the following GPUs:

- Cape Verde (DCE 6): affected
- Tonga (DCE 10): affected
- Polaris (DCE 11.2): not affected
- Vega (DCE 12): not affected

Polaris and Vega are not affected because the same mode
gets rejected by other parts of the code base, possibly the
bandwidth calculation which exists for DCE11+ but not older HW.

It is not documented whether YUV422 is actually supported over DP
on DCE, but considering that this encoding was never used before,
and that YUV420 is already marked unsupported, probably not.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
---
 drivers/gpu/drm/amd/display/dc/dce/dce_link_encoder.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/display/dc/dce/dce_link_encoder.c b/drivers/gpu/drm/amd/display/dc/dce/dce_link_encoder.c
index 0c50fe266c8a..686f6be68c91 100644
--- a/drivers/gpu/drm/amd/display/dc/dce/dce_link_encoder.c
+++ b/drivers/gpu/drm/amd/display/dc/dce/dce_link_encoder.c
@@ -798,7 +798,8 @@ bool dce110_link_encoder_validate_dp_output(
 	const struct dce110_link_encoder *enc110,
 	const struct dc_crtc_timing *crtc_timing)
 {
-	if (crtc_timing->pixel_encoding == PIXEL_ENCODING_YCBCR420)
+	if (crtc_timing->pixel_encoding == PIXEL_ENCODING_YCBCR420 ||
+		crtc_timing->pixel_encoding == PIXEL_ENCODING_YCBCR422)
 		return false;
 
 	return true;
-- 
2.51.0