[Intel-gfx] [PATCH 3/3] drm/i915/userptr: Enable read-only support on gen8+

[Chris Wilson]

Quoting Chris Wilson (2018-05-31 10:19:23)
> On gen8 and onwards, we can mark GPU accesses through the ppGTT as being
> read-only, that is cause any GPU write onto that page to be discarded
> (not triggering a fault). This is all that we need to finally support
> the read-only flag for userptr!

For full disclosure, I should say I have some caveats about ro support
around the API: I think both pwrite and GGTT mmap should reject bogus
writes. Hmm, indeed in this case, GGTT mmap will explode.
-Chris