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

[Jiri Kosina]

On Sat, 30 Dec 2017, Jiri Kosina wrote:

> Seems like disabling RC6 on the kernel command line works this around, and 
> I can dock / undock several times in a row with the image always coming 
> up properly on the external display.
> 
> On the first undock, the WARN_ONCE() below triggers, so I believe each 
> undock leaks memory.
> 
> [   38.755084] Failed to release pages: bind_count=1, pages_pin_count=1, pin_global=0
> [   38.755138] WARNING: CPU: 3 PID: 96 at ../drivers/gpu/drm/i915/i915_gem_userptr.c:89 cancel_userptr+0xe5/0xf0 [i915]

OK, I am seeing this warning with current Linus' tree (5aa90a845) even 
without any attempt to dock/undock, so it's probably unrelated to external 
outputs and it only by coincidence appeared originally at the same time I 
docked the machine.

So there are two separate issues on this machine with latest kernel 
(neither of them probably being regression):

- I have to disable i915 RC6 at the kernel cmdline, otherwise external 
  (dock) display gets output only randomly (seems like always only on 
  first dock)

- the warning, which triggers at not really deterministic time after boot, 
  but usually rather quickly

-- 
Jiri Kosina
SUSE Labs