[PATCH 1/2] drm/i915: add gem/gt TODO

[Daniel Vetter]

On Tue, Mar 23, 2021 at 12:13:11PM +0200, Jani Nikula wrote:
> On Tue, 23 Mar 2021, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> > We've discussed a bit how to get the gem/gt team better integrated
> > and collaborate more with the wider community and agreed to the
> > following:
> >
> > - all gem/gt patches are reviewed on dri-devel for now. That's
> >   overkill, but in the past there was definitely too little of that.
> >
> > - i915-gem folks are encouraged to cross review core patches from
> >   other teams
> >
> > - big features (especially uapi changes) need to be discussed in an
> >   rfc patch that documents the interface and big picture design,
> >   before we get lost in the details of the code
> >
> > - Also a rough TODO (can be refined as we go ofc) to get gem/gt back
> >   on track, like we've e.g. done with DAL/DC to get that in shape.
> 
> I personally think there should be a lower bar for discussing and
> editing the TODO items than via patches on the mailing list. Granted,
> the TODO file enforces the discussion happens at a large enough
> audience, but for at least some of the items I'd suggest filing gitlab
> issues [1], with todo label, and tracking there.

In general yes, and I'd go even further: it's up to each team/contributor
how they track review feedback and further work, whether that's gitlab or
some notes or just in their heads.

This is a different situation here, and the "changes require big audience"
is a feature, not a bug. But it is a very exceptional situation, I think
this is only the 2nd time we're using a formal TODO for a gpu driver. If
we ignore gma500 in staging, which for me only showed that the separate
staging tree doesn't work so well for complex drivers like we have.
-Daniel

> 
> BR,
> Jani.
> 
> 
> [1] https://gitlab.freedesktop.org/drm/intel/-/issues
> 
> 
> 
> >
> > Cc: Jani Nikula <jani.nikula at linux.intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> > Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > Cc: Jason Ekstrand <jason at jlekstrand.net>
> > Cc: Dave Airlie <airlied at redhat.com>
> > Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> > ---
> >  drivers/gpu/drm/i915/TODO.txt | 36 +++++++++++++++++++++++++++++++++++
> >  1 file changed, 36 insertions(+)
> >  create mode 100644 drivers/gpu/drm/i915/TODO.txt
> >
> > diff --git a/drivers/gpu/drm/i915/TODO.txt b/drivers/gpu/drm/i915/TODO.txt
> > new file mode 100644
> > index 000000000000..d2e5bbb6339d
> > --- /dev/null
> > +++ b/drivers/gpu/drm/i915/TODO.txt
> > @@ -0,0 +1,36 @@
> > +gem/gt TODO items
> > +-----------------
> > +
> > +- For discrete memory manager, merge enough dg1 to be able to refactor it to
> > +  TTM. Then land pci ids (just in case that turns up an uapi problem). TTM has
> > +  improved a lot the past 2 years, there's no reason anymore not to use it.
> > +
> > +- Come up with a plan what to do with drm/scheduler and how to get there.
> > +
> > +- There's a lot of complexity added past few years to make relocations faster.
> > +  That doesn't make sense given hw and gpu apis moved away from this model years
> > +  ago:
> > +  1. Land a modern pre-bound uapi like VM_BIND
> > +  2. Any complexity added in this area past few years which can't be justified
> > +  with VM_BIND using userspace should be removed. Looking at amdgpu dma_resv on
> > +  the bo and vm, plus some lru locks is all that needed. No complex rcu,
> > +  refcounts, caching, ... on everything.
> > +  This is the matching task on the vm side compared to ttm/dma_resv on the
> > +  backing storage side.
> > +
> > +- i915_sw_fence seems to be the main structure for the i915-gem dma_fence model.
> > +  How-to-dma_fence is core and drivers really shouldn't build their own world
> > +  here, treating everything else as a fixed platform. i915_sw_fence concepts
> > +  should be moved to dma_fence, drm/scheduler or atomic commit helpers. Or
> > +  removed if dri-devel consensus is that it's not a good idea. Once that's done
> > +  maybe even remove it if there's nothing left.
> > +
> > +Smaller things:
> > +- i915_utils.h needs to be moved to the right places.
> > +
> > +- dma_fence_work should be in drivers/dma-buf
> > +
> > +- i915_mm.c should be moved to the right places. Some of the helpers also look a
> > +  bit fishy:
> > +
> > +  https://lore.kernel.org/linux-mm/20210301083320.943079-1-hch@lst.de/
> 
> -- 
> Jani Nikula, Intel Open Source Graphics Center

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch