[igt-dev] [PATCH i-g-t 2/2] i915/treewide: Replace gem_mmap__gtt() by gem_mmap__device_coherent()

[Dixit, Ashutosh]

On Sat, 11 Jan 2020 00:44:59 -0800, Chris Wilson wrote:
>
> Here, we want OFFSET_WC etc added. So leave this style for a later patch,
> and focus on just converting the ones where we want any old mapping to
> device_coherent(). Another patch can focus on converting any __cpu maps
> that are only used for writes to device_coherent.

Thanks for the feedback Chris, makes sense, will rework and repost.

Some time ago, Dixit, Ashutosh wrote:
> On Sat, 11 Jan 2020 00:40:32 -0800, Chris Wilson wrote:
> > Quoting Ashutosh Dixit (2020-01-11 05:36:52)
> > > In order to preserve legacy behavior for devices with a mappable
> > > aperture try a GTT mapping first. Use a WC mapping only for devices
> > > without a mappable aperture.
> >
> > No...? It's just historical legacy from before we even had WC available.
> > Since we've had WC for basic mmappings, we prefer WC since it is not as
> > scarce and as precious a resource. (Not that it matters for most tests
> > since GTT thrashing in basic igt is unheard of!)

About this, I was assuming if we were using WC instead of GTT on legacy
(Gen < 6), we would have to set read/write domains to WC too, unless you
are saying it's not required? (From what I know, for later Gen's, setting
the domain to either GTT or WC is identical).