[Bug 91434] [IVB/HSW] 23.976Hz & 24Hz modes broken on dual-display with recent (4.0.x) kernels

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=91434

--- Comment #32 from Martin Andersen <martin.x.andersen at gmail.com> ---
Did some further testing today (wondering why I still bother as this has now
been broken for two whole years), and Intel apparently has utter disregard for
its customers.

Tested with the latest kernel from drm-tip, 4.12.0-994_4.12.0-994. 50 & 60Hz
modes only work intermittently, and with an erratic picture and white dots
showing.

Reverting to either the 24.000Hz or 23.976Hz modes produces a stable picture.

The issue with intermittent output is also present during boot/KMS, indicating
it is probably not an Xorg issue.

Modes tested after boot:

  988  18-Jun-2017 15:10:34 xrandr -q
  990  18-Jun-2017 15:11:05 xrandr --output HDMI2 --mode 1920x1080 --rate
23.976
  991  18-Jun-2017 15:11:21 xrandr -q

  993  18-Jun-2017 15:11:33 xrandr --output HDMI2 --mode 1920x1080 --rate 60
  994  18-Jun-2017 15:11:57 xrandr --output HDMI2 --mode 1920x1080 --rate 50
  995  18-Jun-2017 15:12:20 xrandr --output HDMI2 --mode 1920x1080 --rate 24
  996  18-Jun-2017 15:12:56 xrandr --output HDMI2 --mode 1920x1080 --rate 60
  997  18-Jun-2017 15:13:30 xrandr --output HDMI2 --mode 1920x1080 --rate 50
  998  18-Jun-2017 15:14:02 xrandr --output HDMI2 --mode 1920x1080 --rate
23.976
  999  18-Jun-2017 15:14:15 xrandr --output HDMI2 --mode 1920x1080 --rate 50
 1000  18-Jun-2017 15:14:35 xrandr --output HDMI2 --mode 1920x1080 --rate 60

Kernel debug output with drm.debug=0xe is included as per usual. Maybe it is of
usage to /dev/null

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