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

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Date:   Sat, 30 Dec 2017 13:53:58 +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: Re: Graphics on thinkpad x270 after dock/undock works only for the
 first time (CPU pipe B FIFO underrun)

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