Re: [PATCH v2 0/2] Allow partial memory mapping for cpu memory

[Matthew Brost <matthew.brost@intel.com>]

On Mon, Aug 19, 2024 at 05:16:09PM +0200, Andi Shyti wrote:
> Hi Matt,
> 
> On Wed, Aug 14, 2024 at 04:07:02PM +0000, Matthew Brost wrote:
> > On Wed, Aug 14, 2024 at 03:48:32PM +0200, Andi Shyti wrote:
> > > I am resending this patch series, not to disregard the previous
> > > discussions, but to ensure it gets tested with the IGTs that
> > > Krzysztof has provided.
> > > 
> > > This patch series finalizes the memory mapping fixes and
> > > improvements by enabling partial memory mapping for CPU memory as
> > > well.
> > > 
> > > The concept of partial memory mapping, achieved by adding an
> > > object offset, was implicitly introduced in commit 8bdd9ef7e9b1
> > > ("drm/i915/gem: Fix Virtual Memory mapping boundaries
> > > calculation") for GTT memory.
> > > 
> > > To address a previous discussion with Sima and Matt, this feature
> > > is used by Mesa and is required across all platforms utilizing
> > > Mesa. Although Nirmoy suggested using the Fixes tag to backport
> > 
> > Other vendors than Intel too?
> 
> Yes, that's what I understood.
> 
> I hope Lionel can jump in and explain the use cases from Mesa
> perspective.
> 

Hearing from Lionel would be helpful.

> > > this to previous kernels, I view this as a new feature rather
> > > than a fix.
> > > 
> > > Lionel, please let me know if you have a different perspective
> > > and believe this should be treated as a bug fix, requiring it
> > > to be backported to stable kernels.
> > > 
> > > The IGTs have been developed in collaboration with the Mesa team
> > > to replicate the exact Mesa use case[*].
> > > 
> > > Thanks Chris for the support, thanks Krzysztof for taking care of
> > > the IGT tests, thanks Nirmoy for your reviews and thanks Sima and
> > > Matt for the discussion on this series.
> > > 
> > > Andi
> > > 
> > > [*] https://patchwork.freedesktop.org/patch/608232/?series=137303&rev=1
> > 
> > So here is really quick test [1] which I put together in Xe to test
> > partial mmaps, not as complete as the i915 one though.
> > 
> > It fails on the Xe baseline.
> > 
> > It pass if with [2] in drm_gem.c:drm_gem_mmap. Blindly changing that
> > function might not be the correct solution but thought I'd share as a
> > reference.
> 
> Thanks for sharing it. I took a quick look and I think there are
> a few things missing there. If you want and if this is not in
> anyone's task list, I can try to "port" this in XE.
> 

That would be great as I'm sure you undertstand what needs to be done
the best. Thanks for volunteering here.

> Is there any other objection to getting this merged into i915?
>

No as long as sima is ok with it, and we prioritize this for Xe as I
don't want to remove force probe with an incongruence in behavior from
the i915 or have a mesa use case broken.

Matt

> Andi