[Intel-gfx] [PATCH 2/2] drm/i915: wait for IPS_ENABLE when enabling IPS

[Chris Wilson]

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.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre