[Bug 95176] LCD flickering on Thinkpad T440p (Haswell) with kernel 4.6-rc4 (PSR enabled)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=95176

--- Comment #39 from Calvin Walton <calvin.walton at kepstin.ca> ---
When I re-enable the internal display on my T440p I have the following display
configuration:

- eDP internal display (1920x1080)
- Thinkpad Ultra dock
 |- DP monitor (2560x1440)
 \- HDMI monitor (1920x1080)

Immediately after enabling this configuration, the kernel log printed:
[17481.417387] [drm:intel_set_cpu_fifo_underrun_reporting] *ERROR* uncleared
fifo underrun on pipe B
[17481.417392] [drm:intel_cpu_fifo_underrun_irq_handler] *ERROR* CPU pipe B
FIFO underrun

(I don't presently have any debug logging enabled, will retest with that later)

and the external DP monitor started blanking out for longish periods of time,
up to several seconds (moving the mouse would usually cause the picture to
re-appear.

The external HDMI monitor didn't blank completely, but did appear to lose sync
or display corrupted picture - e.g. horizontal offset, shaking picture.

Disabling psr (with the option i915.enable_psr=0 option) fixes this completely.

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