[Bug 94822] System hangs when some video output is disabled/enabled on Skylake platform in double/triple display configuration

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=94822

--- Comment #4 from Edgar Cherkasov <echerkasov at dev.rtsoft.ru> ---
(In reply to Jim Bride from comment #3)

Hi Jim,

thanks a lot for your feedback!

First of all let me inform your regarding the state of the main
problem(Linux hangs when video output is disabled/enabled during boot) -
it can't be reproduced with vanilla 4.6.rc5 kernel.

And please find answers to your questions below:

> There are a couple of odd things that I’ve seen while looking over the first
> dmesg log.  The first is that the sink devices advertise that they only
> support up to 2.7Gbps transfer rate, which makes me suspect that they are
> older models. Could you please tell us the make and model numbers of the
> displays in question?

This can be caused by our DP to VGA and DP to DVI converters. If needed
I can repeat the test using a "pure" DP display without any converters.
Description of our current h/w configuration:

1) First DDI output -> DP to DVI-I converter(Chrontel CH7318C) -> DVI
display(Acer V223W);

2) Second DDI output -> DP to VGA converter(noname) -> VGA
display(RoverScan JM678);

3) eDP output -> on-board eDP to LVDS converter(PTN3460) -> LVDS
display(LG LB121S03).

> The second is that there are quite a number of
> watermark WARNs.  The kernel log lists the version as 4.6.999, so I really
> don’t have a clue specifically how recent this is, and I have to assume that
> it’s based on the kernel.org kernel. 

These tests were performed with the latest at that time(first days of
April) version of drm-intel-nightly from prebuilt Ubuntu repository:
http://kernel.ubuntu.com/~kernel-ppa/mainline/drm-intel-nightly/
If needed, I can try to find the exact version.

> There have been some fixes in the
> watermarking area recently, so it would be helpful to try and reproduce this
> issue using the same hardware and drm-intel-nightly (assuming this is not
> drm-intel with the version info changed.)

I've tried the latest drm-intel-nightly from the same Ubuntu repository:
cod/tip/drm-intel-nightly/2016-05-05
bbb6a0d936b5648b31f173d47f93f389a6c6b653
and, unfortunately, all the same - system hangs during the execution of
kms_plane test from intel-gpu-tools. The only difference is broken
S3(but it does not relate to Intel drm). Please find logs in the
attachment.

> Finally, although the stated
> reason for the patches referenced in the thread is DP MST, it might be worth
> trying the two attached patches on top of drm-intel-nightly, assuming the
> problem reproduces against that kernel.  The issue being fixed is
> exacerbated by MST, but it is a general racy problem with the frame buffer
> connector counting if I’m interpreting the information correctly.

Thanks! I will give it a try and provide a feedback in 1-2 days.

Summary:
As the problem can't be reproduced on vanilla 4.6.rc5 kernel, the bug
can be closed, but:
 - I still want to test the attached patches and provide feedback;
 - please tell if additional experiments/information are needed(testing
on pure DP display, testing different kernels, different versions of
drm-intel-nightly, ...).

Best regards,
Edgar Cherkasov.

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