[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

Martin Andersen <martin.x.andersen at gmail.com> changed:

           What    |Removed                     |Added
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             Status|NEEDINFO                    |ASSIGNED

--- Comment #34 from Martin Andersen <martin.x.andersen at gmail.com> ---
There is no DP-HDMI dongle involved. The output is fed directly from a MacBook
Retina system via full-size/regular HDMI cable. (Yes, I've also noticed it says
DP.)

However; the exact same setup works 100% correctly with older kernels, as
outlined earlier in the ticket. By 100% i mean: never any picture dropouts,
never any dots (which only were seen with this most recent kernel) or other
graphical glitches.
The main production system (on IVB) currently runs 3.18.5; it behaves the same
with all recent kernel branches also.

I did quite a bit of testing earlier, on two Haswell-based systems and one Ivy
Bridge, with kernels ranging from 4.0.9, 4.8.1, 4.11.0 and most recently
4.12.0. They all exhibit consistent behaviour->none work correctly with
dual-display under any recent kernel.

Bear in mind that the unstable picture reported with this kernel from Jun 17th
2017 was *not* an issue with the prior ones, where it produced a stable 50&60Hz
picture (but no 23.976 or 24.000Hz (hence the title of this bug report) - which
led me to believe someone excplictly tried to fix the film modes between 4.11 &
4.12), but breaking the others in the process (for dual-screen setups).

I have three other sources hooked up to this projector, and none have issues. 
The same behaviour is seen when hooked up directly to either of the projector's
two HDMI ports - with another cable - as well. So I believe 'cabling issues'
can be ruled out.

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