Re: [PATCH 4/4] drm/i915: enable forcewake voodoo also for gen6

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Feb 08, 2012 at 10:00:54AM +0000, Chris Wilson wrote:
> On Wed, 25 Jan 2012 14:04:00 +0100, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> > We still have reports of missed irqs even on Sandybridge with the
> > HWSTAM workaround in place. Testing by the bug reporter gets rid of
> > them with the forcewake voodoo and no HWSTAM writes.
> > 
> > Because I've slightly botched the rebasing I've left out the ACTHD
> > readback which is also required to get IVB working. Seems to still
> > work on the tester's machine, so I think we should go with the more
> > minmal approach on SNB. Especially since I've only found weak evidence
> > for holding forcewake while waiting for an interrupt to arrive, but
> > none for the ACTHD readback.
> > 
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=45181
> > Tested-by: Nicolas Kalkhof nkalkhof()at()web.de
> > Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
> Whilst this patch doesn't directly enable the ACTHD w/a, I have observed
> that with a very light load (drawing a single large transformed texture)
> reading back the ACTHD (along with the GT forcewake dance) becomes the
> predominant consumer of CPU time for the system. (The rate-limiting step
> is still the GPU, it just irked me to see the kernel consume more CPU time
> than X.)
> 
> This workaround appears more successful than the last, and doesn't
> appear to break anything else, so
> 
> Acked-by: Chris Wilson <chris@chris-wilson.co.uk>

I've picked up patches 1,2 & 4 of this series, thanks for taking a look at
them. I'll postpone 3 until we do the seqno/request refactoring for real,
atm there's too much stuff in this area outstanding and we need to judge
this one in the context of the real thing.
-Daniel
-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48