[Intel-gfx] [PATCH 1/2] drm/i915: tune the RC6 threshold for stability

[Stéphane Marchesin]

On Fri, Jun 14, 2013 at 12:32 PM, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> On Fri, Jun 14, 2013 at 9:13 PM, Stéphane Marchesin
> <marcheu at chromium.org> wrote:
>> On Wed, Jun 12, 2013 at 2:41 AM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
>>> On Tue, Jun 11, 2013 at 03:49:26PM -0700, Stéphane Marchesin wrote:
>>>> It's basically the same deal as the RC6+ issues on ivy bridge
>>>> except this time with RC6 on sandy bridge. Like last time the
>>>> core of the issue is that the timings don't work 100% with our
>>>> voltage regulator. So from time to time, the kernel will print
>>>> a warning message about the GPU not getting out of RC6. In
>>>> particular, I found this fairly easy to reproduce during
>>>> suspend/resume.
>>>>
>>>> Changing the threshold to 150000 instead of 50000 seems to fix
>>>> the issue.
>>>>
>>>> I also measured the idle power usage before/after this patch and
>>>> didn't see a difference on a sandy bridge laptop.
>>>>
>>>> Signed-off-by: Stéphane Marchesin <marcheu at chromium.org>
>>>
>>> One magic number for another with no idea what is blowing up - I fear we
>>> are just changing the frequency of the hang. I've pinged a number of snb
>>> rc6 bug reports to see if we get a bite.
>>
>> Yup, if only Intel documented those registers :)
>
> We've spammed rc6 bugs in bugzilla, one reporter says that this patch
> breaks rc6 from "sometimes it doesn't work after resume" to "always
> broken":
>
> https://bugs.freedesktop.org/show_bug.cgi?id=54089#c63
>
> So I guess I can't merge this :(

Yeah I was actually going to send an email to withdraw this patch, as
it prevents rc6 from working on some machines here. So I guess I found
out the same thing.

Stéphane