[Intel-gfx] Graphics on thinkpad x270 after dock/undock works only for the first time (CPU pipe B FIFO underrun)

[Jiri Kosina]

On Fri, 29 Dec 2017, Jiri Kosina wrote:

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

[1] 00:02.0 VGA compatible controller: Intel Corporation Skylake GT2 [HD Graphics 520] (rev 07)

> 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.

Forgot to mention: I'm observing this on (and up to) 4.15-rc5

Thanks,

-- 
Jiri Kosina
SUSE Labs