[Intel-gfx] [PATCH 5/8] drm/i915: avoid waking up from PC8 on GMBUS operations

[Daniel Vetter]

On Tue, Jul 30, 2013 at 10:30:41AM +0100, Chris Wilson wrote:
> On Mon, Jul 29, 2013 at 05:48:24PM -0300, Paulo Zanoni wrote:
> > From: Paulo Zanoni <paulo.r.zanoni at intel.com>
> > 
> > If we're already allowing PC8, just don't use the IRQs, so we won't
> > need to wake from PC8. Waking up from PC8 is a slow thing, so avoid it
> > when we can.
> 
> You would also need to explain that the GMBUS is outside of the display
> power well.
> 
> Looks reasonable, the only bit is moving the read of forbid_count into
> hsw_pc8_enabled() so that the gmbus code isn't poking around with
> someone else's locks, and we can safely do an unlocked optimistic read
> here.

IIrc EDID reads with interrupts take 22ms, without them they can easily
take 100ms. Is pc8+ exit indeed longer than that difference?

If the issue is that we flip-flop between pc8+ allow/deny too often then
we could just add a slight delay.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch