Re: [PATCH 3/7] drm/vc4: Mimic drm_atomic_helper_commit() behavior

[Boris Brezillon <boris.brezillon-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>]

+Gustavo

On Tue, 06 Jun 2017 13:27:09 -0700
Eric Anholt <eric-WhKQ6XTQaPysTnJN9+BGXg@public.gmane.org> wrote:

> Boris Brezillon <boris.brezillon-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org> writes:
> 
> > The VC4 KMS driver is implementing its own ->atomic_commit() but there
> > are a few generic helpers we can use instead of open-coding the logic.
> >
> > Signed-off-by: Boris Brezillon <boris.brezillon-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
> > ---
> >  drivers/gpu/drm/vc4/vc4_kms.c | 38 ++++++++++++--------------------------
> >  1 file changed, 12 insertions(+), 26 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/vc4/vc4_kms.c b/drivers/gpu/drm/vc4/vc4_kms.c
> > index ad7925a9e0ea..f229abc0991b 100644
> > --- a/drivers/gpu/drm/vc4/vc4_kms.c
> > +++ b/drivers/gpu/drm/vc4/vc4_kms.c
> > @@ -42,6 +42,10 @@ vc4_atomic_complete_commit(struct vc4_commit *c)
> >  	struct drm_device *dev = state->dev;
> >  	struct vc4_dev *vc4 = to_vc4_dev(dev);
> >  
> > +	drm_atomic_helper_wait_for_fences(dev, state, false);
> > +
> > +	drm_atomic_helper_wait_for_dependencies(state);  
> 
> With this wait_for_fences() addition and the reservation stuff that
> landed, I think we can rip out the "seqno cb" in vc4, and just use
> drm_atomic_helper_commit() and drm_atomic_hepler_commit_tail().  Do you
> see anything missing, with that?

We can probably get rid of "seqno cb", but I'm not sure we have
everything in place to use drm_atomic_helper_commit_tail() and
drm_atomic_helper_commit() yet.

What about async page flips? The async_modeset semaphore is taken in
vc4_atomic_commit() to prevent races with async page flips. Can we
safely get rid of this? Would Gustavo's work on async plane update help
us get rid of this semaphore?

Also note that patch 4 replaces the call to
drm_atomic_helper_wait_for_vblanks() by one to
drm_atomic_helper_wait_for_flip_done(), and we haven't decided yet if
this is something we want to make generic.



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