[Bug 97099] Regression in 9ef8537e6 "drm/radeon: don't use fractional dividers on RS[78]80 if SS is enabled" (RV620)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97099

            Bug ID: 97099
           Summary: Regression in 9ef8537e6 "drm/radeon: don't use
                    fractional dividers on RS[78]80 if SS is enabled"
                    (RV620)
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Radeon
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: jsagarribay at gmail.com

Created attachment 125352
  --> https://bugs.freedesktop.org/attachment.cgi?id=125352&action=edit
Partial revert of the problematic commit

According to the patch summary it shouldn't affect my system (Mobility Radeon
HD3470, RV620) but it causes artifacts resembling moving waves in the displayed
image and maybe also a headache.

Reverting the second hunk in the patch is enough to get it working again (I'll
attach the revert).

Bisect log:

# bad: [523d939ef98fd712632d93a5a2b588e477a7565e] Linux 4.7
# good: [2dcd0af568b0cf583645c8a317dd12e344b1c72a] Linux 4.6
git bisect start 'v4.7' 'v4.6' '--' 'drivers/gpu/drm/radeon'
# good: [95306975e9dd38ba2775dd96cb29987ecc7d9360] Merge tag
'drm/tegra/for-4.7-rc1' of git://anongit.freedesktop.org/tegra/linux into
drm-next
git bisect good 95306975e9dd38ba2775dd96cb29987ecc7d9360
# good: [84787c572d402644dca4874aba73324d9f8e3948] Merge branch 'akpm' (patches
from Andrew)
git bisect good 84787c572d402644dca4874aba73324d9f8e3948
# good: [79b3c7164c18e2fe9e69b0dcc0d45bab7ae3c968] Merge branch 'drm-next-4.7'
of git://people.freedesktop.org/~agd5f/linux into drm-next
git bisect good 79b3c7164c18e2fe9e69b0dcc0d45bab7ae3c968
# good: [ccaa2c12fba72f3e547d18e66820e2e6c5883113] drm/radeon: do not hard
reset GPU while freezing on r600/r700 family
git bisect good ccaa2c12fba72f3e547d18e66820e2e6c5883113
# bad: [9ef8537e68941d858924a3eacee5a1945767cbab] drm/radeon: don't use
fractional dividers on RS[78]80 if SS is enabled
git bisect bad 9ef8537e68941d858924a3eacee5a1945767cbab
# first bad commit: [9ef8537e68941d858924a3eacee5a1945767cbab] drm/radeon:
don't use fractional dividers on RS[78]80 if SS is enabled

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