[Intel-gfx] [PATCH 1/2] drm/i915/execlists: HWS is uncached on !llc platforms

[Ville Syrjälä]

On Fri, Oct 23, 2015 at 07:29:08PM +0100, Chris Wilson wrote:
> On Fri, Oct 23, 2015 at 09:22:38PM +0300, Ville Syrjälä wrote:
> > On Fri, Oct 23, 2015 at 06:56:41PM +0100, Chris Wilson wrote:
> > > On Fri, Oct 23, 2015 at 08:50:42PM +0300, Ville Syrjälä wrote:
> > > > On Fri, Oct 23, 2015 at 06:43:31PM +0100, Chris Wilson wrote:
> > > > > As the HWS is mapped into the GPU as uncached,
> > > > 
> > > > Since when?
> > > 
> > > Since it is embedded into execlists' default context which is allocated
> > > using the system default cache level, i.e. uncached on !llc. See
> > > intel_lr_context_deferred_alloc()
> > 
> > Oh right. That doesn't actually matter since it's mapped through ggtt
> > which means it always goes through PAT 0.
> 
> Oh, that again. Doesn't that mean we broke i915.enable_ppgtt=0?

Just means everything is snooped in that case. As long as the hardware
doesn't get too upset about all the snooping it should work. Can't
really recall if I actually tried it though. I think I did.

-- 
Ville Syrjälä
Intel OTC