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

[Jesse Barnes]

On Tue, 21 Oct 2014 16:50:12 +0300
Ville Syrjälä <ville.syrjala at linux.intel.com> wrote:

> 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.

Yeah we had that awhile back iirc, but I think it got bikeshedded to
death.  I'd be happy if someone resurrected it; I'd give it an r-b
without suggesting more sophisticated checksum algorithms. :)

http://lists.freedesktop.org/archives/intel-gfx/2012-September/020305.html

Jesse