Re: [PATCH v5 16/20] drm/msm: Don't break exclusive fence ordering

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Aug 26, 2021 at 09:16:25AM -0700, Rob Clark wrote:
> On Thu, Aug 5, 2021 at 3:47 AM Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> >
> > There's only one exclusive slot, and we must not break the ordering.
> >
> > Adding a new exclusive fence drops all previous fences from the
> > dma_resv. To avoid violating the signalling order we err on the side of
> > over-synchronizing by waiting for the existing fences, even if
> > userspace asked us to ignore them.
> >
> > A better fix would be to us a dma_fence_chain or _array like e.g.
> > amdgpu now uses, but
> > - msm has a synchronous dma_fence_wait for anything from another
> >   context, so doesn't seem to care much,
> > - and it probably makes sense to lift this into dma-resv.c code as a
> >   proper concept, so that drivers don't have to hack up their own
> >   solution each on their own.
> >
> > v2: Improve commit message per Lucas' suggestion.
> >
> > Cc: Lucas Stach <l.stach@pengutronix.de>
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > Cc: Rob Clark <robdclark@gmail.com>
> > Cc: Sean Paul <sean@poorly.run>
> > Cc: linux-arm-msm@vger.kernel.org
> > Cc: freedreno@lists.freedesktop.org
> 
> a-b

Also pushed to drm-misc-next, thanks for review&testing.
-Daniel

> 
> > ---
> >  drivers/gpu/drm/msm/msm_gem_submit.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
> > index fb5a2eab27a2..66633dfd58a2 100644
> > --- a/drivers/gpu/drm/msm/msm_gem_submit.c
> > +++ b/drivers/gpu/drm/msm/msm_gem_submit.c
> > @@ -330,7 +330,8 @@ static int submit_fence_sync(struct msm_gem_submit *submit, bool no_implicit)
> >                                 return ret;
> >                 }
> >
> > -               if (no_implicit)
> > +               /* exclusive fences must be ordered */
> > +               if (no_implicit && !write)
> >                         continue;
> >
> >                 ret = drm_sched_job_add_implicit_dependencies(&submit->base,
> > --
> > 2.32.0
> >

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