Re: [REGRESSION 7.3] drm/amd/display: single-frame scanout corruption on DCN32 at 120 Hz since a637a140ab86

[Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>]

The workaround from my previous mail does not survive a suspend.  After
resume from S3 the band was back (seen, not measured) with the TV still
in FreeSync mode, because DC had turned SubVP back on.

Snapshots of amdgpu_dm_capabilities, pp_dpm_mclk and the DTN log, all
at 3840x2160@120 with FreeSync enabled (vrr_range 40-120, the EDID
byte-identical in every snapshot):

  after boot                    sub-viewport disabled, UCLK at 1249 MHz
  20 s after rtcwake -m mem     sub-viewport enabled, UCLK switching,
                                watermark set A at the register maximum
  after toggling Night Light    sub-viewport disabled again

dcn32_allow_subvp_high_refresh_rate() keeps SubVP off a single FreeSync
display by reading stream->allow_freesync, but amdgpu_dm sets that
field only on the first flip after a commit, so the modeset forced on
resume is validated without it.  A gamma change makes DC validate the
state again, this time with the field set.  The patch:

  https://lore.kernel.org/all/20261018221726.27259-1-mikhail.v.gavrilov@gmail.com/

With it, SubVP stays disabled across rtcwake -m mem.  Until it is
merged, toggling Night Light after resume restores the workaround.

None of this changes the band itself: in HDMI VRR mode, and at 100 Hz
in either mode, DC uses SubVP anyway.

-- 
Thanks,
Mikhail