[Intel-gfx] [PATCH 2/2] drm/i915: wait for IPS_ENABLE when enabling IPS
Daniel Vetter
daniel at ffwll.ch
Fri Sep 20 10:12:32 CEST 2013
On Thu, Sep 19, 2013 at 09:24:33PM +0100, Chris Wilson wrote:
> On Thu, Sep 19, 2013 at 05:03:06PM -0300, Paulo Zanoni wrote:
> > From: Paulo Zanoni <paulo.r.zanoni at intel.com>
> >
> > At the end of haswell_crtc_enable we have an intel_wait_for_vblank
> > with a big comment, and the message suggests it's a workaround for
> > something we don't really understand. So I removed that wait and
> > started getting HW state readout error messages saying that the IPS
> > state is not what we expected.
> >
> > I investigated and concluded that after you write IPS_ENABLE to
> > IPS_CTL, the bit will only actually become 1 on the next vblank. So
> > add code to wait for the IPS_ENABLE bit. We don't really need this
> > wait right now due to the wait I already mentioned, but at least this
> > one has a reason to be there, while the other one is just to
> > workaround some problem: we may remove it in the future.
> >
> > The wait also acts as a POSTING_READ which we missed.
> >
> > Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
>
> Both patches:
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
>
> I was thinking that maybe the intel_wait_for_vblank would be better from
> a documenting perspective - and it would also give warnings for trying
> to enable ips whilst the pipe was off. But you would still need the wait
> for IPS_ENABLE as confirmation anyway.
Both queued for -next, thanks for the patches&review.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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