[Intel-gfx] [PATCH 14/19] drm: Don't update vblank timestamp when the counter didn't change

[Mario Kleiner]

On 23/09/14 15:51, Daniel Vetter wrote:
> On Tue, Sep 23, 2014 at 03:48:25PM +0300, Jani Nikula wrote:
>> On Mon, 15 Sep 2014, Daniel Vetter <daniel at ffwll.ch> wrote:
>>> On Sat, Sep 13, 2014 at 06:25:54PM +0200, Mario Kleiner wrote:
>>>> The current drm-next misses Ville's original Patch 14/19, the one i first
>>>> objected, then objected to my objection. It is needed to avoid actual
>>>> regressions. Attached a trivially rebased (v2) of Ville's patch to go on top
>>>> of drm-next, also as tgz in case my e-mail client mangles the patch again,
>>>> because it's one of those "email hates me" weeks.
>>>
>>> Oh dear, I've made a decent mess of all of this really. Picked up to make
>>> sure it doesn't get lost again.
>>
>> After all this nice ping pong our QA has reported a bisected regression
>> on this commit: https://bugs.freedesktop.org/show_bug.cgi?id=84161
>
> Looks like a minuscule timing change which resulted in us detecting a fifo
> underrun. Or at least I don't see any other related information that would
> indicate otherwise ...
> -Daniel
>

There's nothing in that code path which could cause this - except for 
altered execution timing. I've seen that warning as well on my Intel HD 
Ironlake Mobile (MBP 2010), but only spuriously when plugging/unplugging 
an external display into the laptop iirc, so i thought it would be 
unrelated.

-mario