[Bug 71267] sna: (Haswell) X-server freezes when enabling DP at docking station

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=71267

--- Comment #26 from Daniel Martin <consume.noise at gmail.com> ---
Created attachment 90101
  --> https://bugs.freedesktop.org/attachment.cgi?id=90101&action=edit
dmesg 3.13.0-rc1 with hack from comment #24

dmesg 3.13.0-rc1 with:
- hack from comment #24
- DRM_DEBUG_KMS messages before, inside and when leaving a lock on
mode_config.mutex
- DRM_DEBUG_KMS messages before schedule/cancel_delayed_work(_sync) on
panel_vdd_work (That's why "XXX: schedule work (msecs_to_jiffies)..." shows
up.)

I've to recall my statement in comment #24:
> I know that's not atomic. But, in case of the bug it runs into the if-clause (so, the mutex is locked) and gives a warning about an unbalanced unlock. Then it moves on and ironlake_panel_vdd_work() gets stuck when trying to lock mode_config.mutex.

With the hack applied it doesn't deadlock in ironlake_panel_vdd_work() when
aquiring the lock on mode_config.mutex. Comparing the dmesg output with the
preemption workaround, see attachment #89947, I miss
intel_dp_set_signal_levels() and friends between haswell_write_eld() and
ironlake_panel_vdd_work().

Notes on dmesg:
@57.286024 I've plugged in the monitor and wait.

@263.064377 More than 120s are gone and no "task kworker/xyz blocked for more
than 120 seconds" message showed up. Try to start Xorg and wait.

@480.271406 "INFO: task Xorg:152 blocked for more than 120 seconds." Yep, last
message in Xorg.0.log is "xfree86: Adding drm device (/dev/dri/card0)". The
nice retro pattern never showed up. ;)

@480.307359 "INFO: lockdep is turned off." Heee? I've definitly enabled
lockdep, made a `make clean && make` in the kernel tree and in /proc/config.gz
I can find CONFIG_LOCKDEP=y.

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