[Intel-gfx] [RFC 33/60] drm/i915/lmem: support pwrite

[Joonas Lahtinen]

Quoting Dave Airlie (2020-07-13 08:09:30)
> On Fri, 10 Jul 2020 at 22:00, Matthew Auld <matthew.auld at intel.com> wrote:
> >
> > We need to add support for pwrite'ing an LMEM object.
> 
> why? DG1 is a discrete GPU, these interfaces we already gross and
> overly hacky for integrated, I'd prefer not to drag them across into
> discrete land.
> 
> same goes for pread.
> 
> You have no legacy userspace here, userspace needs change to support
> LMEM, it can be fixed to avoid legacy ioctls paths.

(This answer is really along the same lines as related to the
relocations, which I sent earlier in the end of this thread)

PREAD/PWRITE are used by IGT tests indirectly in the testing, as
a means to validate test end results as an example. So IGT
reworking is needed not to lose testing coverage when the
functionality is disabled.

Same reasoning as with relocations, as to why this is included
in the RFC; it will get a functional stack with least changes and
is virtually no extra effort to carry. It's recognized that once
pre-Gen12 hardware ceases to exist, there are optimization
opportunities.

Based on the feedback to this Request for Comments series, we are
expediting the work on those IGT reworks.

Regards, Joonas