On Fri, Sep 19, 2025 at 4:14 AM Timur Kristóf <[email protected]> wrote:
>
> 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 <[email protected]>
Fixes: db291ed1732e02 ("drm/amd/display: Add fallback path for YCBCR422")
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4585
Acked-by: Alex Deucher <[email protected]>
Would be good to get feedback from the display team on what the actual
capabilities are, but seems reasonable to me.
Alex
> ---
> 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
>
