On Fri, Feb 27, 2026 at 08:20:10PM +0100, Nicolas Frattaroli wrote:
> drm_hdmi_connector_mode_valid assumes modes are only valid if they work
> with RGB. The reality is more complex however: YCbCr 4:2:0
> chroma-subsampled modes only require half the pixel clock that the same
> mode would require in RGB.
>
> This leads to drm_hdmi_connector_mode_valid rejecting perfectly valid
> 420-only or 420-also modes.
>
> Fix this by checking whether the mode is 420-capable first. If so, then
> proceed by checking it with DRM_OUTPUT_COLOR_FORMAT_YCBCR420 so long as
> the connector has legalized 420, otherwise error out. If the mode is not
> 420-capable, check with RGB as was previously always the case.
>
> Fixes: 47368ab437fd ("drm/display: hdmi: add generic mode_valid helper")
> Reviewed-by: Maxime Ripard <[email protected]>
> Signed-off-by: Nicolas Frattaroli <[email protected]>
> ---
> drivers/gpu/drm/display/drm_hdmi_state_helper.c | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
Reviewed-by: Dmitry Baryshkov <[email protected]>
--
With best wishes
Dmitry
