[Intel-gfx] [PATCH 5/5] drm/i915/userptr: Enable read-only support on gen8+

[Chris Wilson]

Quoting Joonas Lahtinen (2018-06-01 11:21:43)
> On Thu, 2018-05-31 at 12:35 +0100, Chris Wilson wrote:
> > 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!
> > 
> > Testcase: igt/gem_userptr_blits/readonly*
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Jon Bloomfield <jon.bloomfield at intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> 
> Please add clarification to the commit message that this expands uAPI
> (by supporting RO userptrs), so Rodrigo will notice to highlight for
> -next PR.

Ha, I was playing the "this was already in the uAPI" card,
just never implemented so hadn't made it in the uABI. :)

Being able to import read-only shm segments (or PROT_READ file mmaps)
was always on my wishlist, just at the time the only prospect was
special case supporting it for byt (not very appealing).

PR material it is then.
-Chris