[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 #26 from Martin Andersen <martin.x.andersen at gmail.com> ---
Ok - well, this was interesting. Now the situation as initially reported in the
bug is reversed: 24.00Hz & 23.976Hz modes work(!), however 50 & 60Hz modes
(which previously were the only ones to be outputted) *do not*. No output is
seen from the virtual terminal either.

Including debug output from my Haswell-based system. The steps taken after boot
are as follows:

martin at meraxes ~ $ xrandr --output HDMI2 --mode 1920x1080 --rate 24
(works!)

martin at meraxes ~ $ xrandr -q

martin at meraxes ~ $ xrandr --output HDMI2 --mode 1920x1080 --rate 23.976
(works!)

martin at meraxes ~ $ xrandr -q
martin at meraxes ~ $ xrandr --output HDMI2 --mode 1920x1080 --rate 60
(no signal)

martin at meraxes ~ $ xrandr --output HDMI2 --mode 1920x1080 --rate 50
(no signal)

martin at meraxes ~ $ xrandr -q
martin at meraxes ~ $ xrandr --output HDMI2 --mode 1920x1080 --rate 30
(30Hz, curiously, also works)

martin at meraxes ~ $ xrandr --output HDMI2 --mode 1920x1080 --rate 59.9
(no signal)

martin at meraxes ~ $ xrandr --output HDMI2 --mode 1920x1080 --rate 23.976
(works)

martin at meraxes ~ $ xrandr -q
martin at meraxes ~ $ xrandr --output HDMI2 --mode 1920x1080 --rate 50
(no signal after trying to switch for 10 secs)

martin at meraxes ~ $ xrandr -q
martin at meraxes ~ $ xrandr --output HDMI2 --mode 1920x1080 --rate 24
(works)

martin at meraxes ~ $ xrandr --output HDMI2 --mode 1920x1080 --rate 60
(no signal)

martin at meraxes ~ $ xrandr -q
martin at meraxes ~ $ xrandr --output HDMI2 --mode 1920x1080 --rate 23.976
(works)


The 23.976Hz mode is the rightmost on the 1920x1080 list given by xrandr;

$ xrandr -q

HDMI2 connected 1920x1080+2560+0 (normal left inverted right x axis y axis) 0mm
x 0mm
   1920x1080      60.0 +   50.0     59.9     24.0     24.0*
   1920x1080i     60.1     50.0     60.0
   1280x720       60.0     50.0     59.9
   1440x576       50.0
   1440x480       60.0     59.9
   720x576        50.0
   720x576i       50.1
   720x480        60.0     59.9
   720x480i       60.1     60.1
   640x480        60.0     59.9
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

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