[Intel-gfx] [PATCH 08/16] drm/i915: remove unused restore_gtt_mappings optimization during suspend

[Ville Syrjälä]

On Thu, Sep 11, 2014 at 07:15:27AM -0700, Jesse Barnes wrote:
> On Thu, 11 Sep 2014 14:59:35 +0300
> Imre Deak <imre.deak at intel.com> wrote:
> 
> > On Thu, 2014-09-11 at 08:49 +0100, Chris Wilson wrote:
> > > On Wed, Sep 10, 2014 at 06:17:01PM +0300, Imre Deak wrote:
> > > > Since correctness wins over optimal code and since the optimization
> > > 
> > > Optimal code is also correct ;-) s/optimal/just plain broken/
> > 
> > Yes, bad wording. To clarify, since the optimization is now always off
> > anyway (and it's also broken), I would hope that we could remove it for
> > now and concentrate on fixing the existing s/r issues. Once we find that
> > things are stable enough we could add back this optimization.
> 
> Arg, I guess we didn't test after moving to the opregion test?  Or maybe
> it was working when it landed for S3 and not for S4?  Or broke sometime
> after it landed?
> 
> Anyway this is a really valuable optimization for resume time on some
> platforms, and really we shouldn't have other agents clobbering our GTT
> on resume, so I'd really like to fix/re-add it asap.

If/when we add this back I would suggest that we also add a sanity check
that can be enabled with drm.debug which would verify the GTT mapping
are what we expect. That way at least most developer would have it
enabled and we'd catch problems earlier, and also bug reporters would
be forced to enable it when we ask for dmesg w/ debugs.

-- 
Ville Syrjälä
Intel OTC