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

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

On 9/19/25 17:09, Alex Deucher wrote:
> On Fri, Sep 19, 2025 at 4:14 AM Timur Kristóf <timur.kristof@gmail.com> 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 <timur.kristof@gmail.com>
> 
> Fixes: db291ed1732e02 ("drm/amd/display: Add fallback path for YCBCR422")
> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4585
> Acked-by: Alex Deucher <alexander.deucher@amd.com>
> 
> Would be good to get feedback from the display team on what the actual
> capabilities are, but seems reasonable to me.
> 
> Alex


Please disregard this patch.

I will send a different patch which will instead reject modes that would 
require a pixel clock higher than the maximum display clock.

Thanks,
Timur