[Bug 79311] Call trace originating from i915 referencing intel_wait_for_vblank()

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=79311

Alan Bartlett <ajb at elrepo.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|CODE_FIX                    |---

--- Comment #30 from Alan Bartlett <ajb at elrepo.org> ---
(In reply to Jani Nikula from comment #29)
> Fix pushed to drm-intel-fixes:
> 
> commit 7a98948f3b536ca9a077e84966ddc0e9f53726df
> Author: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Date:   Mon Sep 8 17:43:01 2014 +0300
> 
>     drm/i915: Wait for vblank before enabling the TV encoder
> 
> Thanks for the report and testing.

Unfortunately that patch does not provide a full fix.

Some further background information: 

The hardware, a Dell Latitude E5500, is configured to dual boot either RHEL-6
or RHEL-7. The relevant lines output by a 'lspci -nnv' command which defines
the video subsystem is attached.

The linux-3.17-rc4 source was used, the above patch was applied and two kernels
were built, one for the RHEL-6 system and another for the RHEL-7 system.

3.17.0-0.rc4.bcat.el6.elrepo.x86_64
3.17.0-0.rc4.bcat.el7.elrepo.x86_64

The RHEL-6 system generates a trace that refers to
"g4x_wait_for_vblank+0xd5/0xf0 [i915]()", "vblank wait timed out" and also
mentions "*ERROR* pipe A underrun".

The RHEL-7 system generates a trace that refers to
"intel_wait_for_vblank+0x209/0x210 [i915]()", "vblank wait timed out".

Both traces, suitably labelled, are attached.

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