Re: [PATCH 0/2] drm/amd/display: don't overwrite regamma LUT with empty data

[Melissa Wen <mwen@igalia.com>]

On 22/08/2025 18:14, Melissa Wen wrote:
> Hey,
>
>
> KDE/Plasma users reported some flickering when applying the regamma CRTC
> LUT to an AMD display hardware set using an external or integrated
> screen. There is some instability in how the driver stores and updates
> color blocks based on color management changes or full update request.
> It uses update_flag bits for surface and stream and forces some color
> blocks to update without considering the previous settings.
>
> This two-patch series avoids this issue by
> (1) not calling set_output_transfer_func when the output TF has not
> changed;
> (2) preserve the previous out_tf value in the case of a full
> update, which was unconditionally setting all update_flag bits to true
> regardless of previous values.
>
> This modifies DC and may affect behavior on other platforms. On the
> other hand, it avoids unnecessary reprogramming of MPC output gamma.
I linked in each patch but better refer the AMD issue here too:
- https://gitlab.freedesktop.org/drm/amd/-/issues/4444
>
> Melissa
>
> Melissa Wen (2):
>    Revert "drm/amd/display: program output tf when required"
>    drm/amd/display: don't update out gamma if out_tf didn't change
>
>   drivers/gpu/drm/amd/display/dc/core/dc.c                | 5 +++++
>   drivers/gpu/drm/amd/display/dc/hwss/dcn20/dcn20_hwseq.c | 5 +----
>   2 files changed, 6 insertions(+), 4 deletions(-)
>