[Intel-gfx] [PATCH] drm/i915/gem: Ensure aperture exists before setting domain to GTT

[Chris Wilson]

Quoting Summers, Stuart (2019-11-19 22:58:38)
> On Tue, 2019-11-19 at 22:08 +0000, Chris Wilson wrote:
> > Quoting Stuart Summers (2019-11-19 21:30:32)
> > > mmap_gtt is already covered by a check for aperture presence.
> > > Also add the case to the gem_set_domain IOCTL to avoid this
> > > path for unsupported platforms.
> > 
> > It doesn't harm either, it will just mean in a place where it is
> > neither
> > in the GPU nor in the CPU cache, same as it does today. The
> > additional
> > flushes coming out of a GTT write domain should already be elided.
> > 
> > It is used internally to mean precisely that...
> > 
> > Userspace should already be weaning itself off set-domain altogether.
> 
> But even with the weaning, shouldn't we have these checks in place for
> safety? Let's say there's some platform issue with the GTT flushes and
> moving ahead causes the hardware to get in a bad state. Isn't it better
> to bail early? Let me know if I'm missing something obvious here
> though.

That we use it internally.

It will never be unsafe simply because if the extra flushes don't exist,
they don't exist. Just like today!
-Chris