Re: [PATCH 2/2] drm/i915: Wait for pending flips in intel_pipe_set_base()

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Oct 31, 2012 at 05:43:16PM +0000, Chris Wilson wrote:
> On Wed, 31 Oct 2012 19:38:41 +0200, ville.syrjala@linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > intel_pipe_set_base() never actually waited for any pending page flips
> > on the CRTC. It looks like it tried to, by calling intel_finish_fb() on
> > the current front buffer. But the pending flips were actually tracked
> > in the BO of the previous front buffer, so the call to intel_finish_fb()
> > never did anything useful.
> > 
> > Now even the pending_flip counter is gone, so we should just
> > use intel_crtc_wait_for_pending_flips(), but since we're already holding
> > struct_mutex when we would call that function, we need another version
> > of it, that itself doesn't lock struct_mutex.
> 
> That function call is now superfluous as you pointed out in an earlier
> review...

I think we still need it when we're not doing a full modeset.
Without it, intel_pipe_set_base() could overtake the flip.

So the call could be moved outside of intel_pipe_set_base() so that
it wouldn't be called for the full modeset path. But I suppose it's
a bit more efficient to do it after we've pinned the new buffer,
so simply moving it might not be the best idea.

> But yes, not waking up the pending_flip_queue after a GPU hang is a
> recent bug, and could explain the lockup in
> https://bugs.freedesktop.org/show_bug.cgi?id=56337.

OK. I suppose I'll cook up a quick patch for that as well.

-- 
Ville Syrjälä
Intel OTC