[PATCH] [Karmic SRU] [Lucid] drm/i915: Fix sync to vblank when VGA output is turned off

[Stefan Bader]

Alberto Milone wrote:
> Hi all,
> 
> SRU Justification:
> 
> The problem described in this email was reported in a private OEM bug report 
> for Dell and has been solved by upstream. It's a regression in the drm code 
> which causes a massive system slowdown if we turn off the VGA output.
> 
> The patch is sane and minimal and is available in the drm-intel branch and in 
> the linux-next branch (see the link to the commit in the bug report).
> 
> I have applied (and slightly adapted, as it didn't apply cleanly to our lucid 
> and karmic git branches) and tested the patch successfully in Karmic.
> 
> The integration of this patch is very important for our Dell projects and for 
> the Ubuntu desktop at large.
> 
> Please include the attached patch in both Karmic and Lucid ASAP.
> 
> Bug #494461
> 
> Thanks in advance for your time.
> 
> Regards,
> 
> 
This should actually have gone to stable as well as it fixes a regression. Also
the description sounds like the integration path should be stable as well (as
long as that is open).
The patch itself looks like it changes semantics of an exported function. Before
additional calls to drm_vblank_get() would return ok and increment the ref count.
After the change, additional calls will return an error and not increment the
count. On the good side it seems that function is only used within drm_irq.c and
the usage seems to be ok to handle that change.
Currently not 100% convinced to ack, but might get convinced.

-Stefan

-Stefan