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

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

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

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

pavol@klacansky.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pavol@klacansky.com

--- Comment #1 from pavol@klacansky.com ---
*** Bug 97138 has been marked as a duplicate of this bug. ***

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

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

--- Comment #2 from Jaime Velasco Juan <jsagarribay@gmail.com> ---
CCed author as it seems the regression hasn't been noticed

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

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

--- Comment #3 from Christian König <deathsimple@vodafone.de> ---
I've noticed this bug, I'm just not sure what to do about it.

Essentially disabling fractional dividers for spread spectrum fixes the output
for some people while it broke it for others.

I will prepare a patch to only apply it for RS780 and RS880 for now, cause
those seem to be the most problematic ones.

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

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

Christian König <deathsimple@vodafone.de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
 Attachment #125352|0                           |1
        is obsolete|                            |

--- Comment #4 from Christian König <deathsimple@vodafone.de> ---
Created attachment 125738
  --> https://bugs.freedesktop.org/attachment.cgi?id=125738&action=edit
Possible fix

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

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

--- Comment #5 from Jaime Velasco Juan <jsagarribay@gmail.com> ---
Thanks, the patch fixes the problem for me, as expected. I hope it doesn't
break other setups. I understand having to lose time with these kind of
workarounds must be very frustrating.

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

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

Christian König <deathsimple@vodafone.de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #6 from Christian König <deathsimple@vodafone.de> ---
Thanks for testing.

Yeah, it's especially tricky when the hardware is already a couple of years old
and even the people who created it don't remember all the nasty details.

The patch should show up in the next kernel release.

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

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

--- Comment #7 from alexeytech@gmail.com ---
provided patch works for me too, thanks. (radeon rv620 HD3450)

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

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

--- Comment #8 from Alex Deucher <alexdeucher@gmail.com> ---
Applied upstream:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=ae5b80d2b68eac945b124227dea34462118a6f01

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

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

Christian König <deathsimple@vodafone.de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |CLOSED

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