[Intel-gfx] Hardlock problems when switching monitor channels and questions (Skylake)

[Maarten Maathuis]

Hi everyone.

I've been some hardlock problems when switching from the HDMI connection of
my monitor (connected to another PC) and the displayport (connected to the
problematic PC), several times a week at least.

In an effort to narrow down the problem I've been tried looking at drm
modeset debug information, as well try catch something with netconsole.
Neither have pointed me the root cause yet, but i do have some observations
that I cannot put into place yet and would like some feedback on prior to
opening a bug report.

My mainbord is: Asrock Fatal1ty Z170 Gaming-ITX/ac
My CPU is: Intel i7 6700
My monitor is: Samsung U24E850, equiped with both displayport 1.2 and HDMI
2.0

Kernel version: 4.3-RC7

The display connections on the mainbord are:
- DP 1.2
- HDMI 1.4
- HDMI 2.0 via DP 1.2 (recognized as DP by driver)

I notice some funny things I would like some feedback on.

1. The EDID retrieval doesn't always succeed, i've noticed this sometimes
by running "xrandr" after starting up. I've also noticed it after rebooting
from a hard lock that it goes into 1024x768 resolution instead of
3840x2160, it takes another reboot to get it right. As if it relies on the
resolution the boot used? How to troubleshoot this?

2. I notice that the driver thinks there are 3 HDMI connections, 2 of which
seem to share the same hotplug pin as the 2 DP connections, what is going
here? Could this cause trouble? The fake HDMI connections seem always to
fail edid retrieval, but I'm not a 100% sure if this also happens in the
hardlock situation (no evidence yet).

3. Switching between HDMI and DP channel on my monitor sometimes results in
a hotplug event and sometimes it does not? Any idea why this happens? I'm
curious about this because the hardlocks occur after spending a few hours
on the HDMI channel typically.

Anything I should be looking for before going down the route of a bug
report?

Sincerely,

Maarten.

P.S. I'm not subscribed to this mailinglist, so please CC me.

-- 
Far away from the primal instinct, the song seems to fade away, the river
get wider between your thoughts and the things we do and say.
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