[Bug 105300] amd-staging-drm-next-git 4.16 & RX 560 DL-DVI: corruption with refreshrates >73Hz when DPM changing VRAM clock

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=105300

            Bug ID: 105300
           Summary: amd-staging-drm-next-git 4.16 & RX 560 DL-DVI:
                    corruption with refreshrates >73Hz when DPM changing
                    VRAM clock
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: tempel.julian at gmail.com

Created attachment 137704
  --> https://bugs.freedesktop.org/attachment.cgi?id=137704&action=edit
edids for 2560x1440 73Hz, 74Hz and 75Hz

Hello,
I tried out amd-staging-drm-next-git with Linux 4.16 and my DL-DVI 2560x1440
display:
Now I finally get a picture and refreshrates below 74Hz seem to work without
apparent issues, thanks for fixing the black screen issue!

However, when using edid information which contains a resolution with
refreshrates higher than 73Hz, I get flickering artifacts on the desktop. The
issue disappears when I force full clocks via sysfs or use display timings
which prevent the VRAM from downclocking. So it seems very likely to me that
it's related to downclocking of the VRAM when using higher refreshrates.
This is a regression, the old display stack (amdgpu.dc=0) works with
refreshrates higher than 73Hz and VRAM downclocking at the same time without
issues.

I attached edid files which can be loaded via drm_kms_helper.edid_firmware and
drm.edid_firmware (they show equal behavior in this case), they use LCD
standard timings.

Thanks!

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