[Bug 93343] WQHD Displayport only 27 Hz

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=93343

--- Comment #6 from Mario Kleiner <mario.kleiner at tuebingen.mpg.de> ---
One thing you could try is booting with the kernel command line parameter
radeon.audio=0 and see if that helps.

I also have some DisplayPort panel from Dell with 2560x1440 native resolution
which runs at 67 Hz refresh rate when the kernel/X-Server/RandR think it is
running at 60 Hz. Setting other than the native resolution will produce too
high or too low refresh rates and/or corrupted display.

Disabling audio over Displayport fixed the problem for me.

The bug there seems to be some misprogramming of clocks or low level mode
timings when audio over Displayport is enabled. This was introduced around
Linux 4.0 with DP audio enablement iirc and might still be an issue in the
current 4.4-rc kernel. I told Alex and Michel about it around that time and
they knew that there might be still work to do to fixup some clock calculations
for DP audio.

-mario

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