linux-kernel - Graphics on thinkpad x270 after dock/undock works only for the first time (CPU pipe B FIFO underrun)

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Date:   Fri, 29 Dec 2017 22:10:22 +0100 (CET)
From:   Jiri Kosina <jikos@...nel.org>
To:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Daniel Vetter <daniel.vetter@...ll.ch>
cc:     intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Graphics on thinkpad x270 after dock/undock works only for the first
 time (CPU pipe B FIFO underrun)

When I dock my thinkpad x270 [1] and run xrandr --auto, image correctly 
appears on external display.

After undocking and docking again, the image on external display doesn't 
appear any more, and this pops up in dmesg

	[drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe B FIFO underrun

After restarting X (no need to reboot), I am able to dock again and get 
image on external display.

I don't think this is a regression, I tried a few older kernels up to 
something around 4.11, and nothing worked.

In case any more information is needed to debug this, please let me know, 
I'll happily provide it.

Thanks,

-- 
Jiri Kosina
SUSE Labs