linux-kernel - Re: [PATCH v9 11/15] drm/atomic-helper: Set fence deadline for vblank

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Date:   Fri, 3 Mar 2023 17:52:02 +0200
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Rob Clark <robdclark@...il.com>
Cc:     dri-devel@...ts.freedesktop.org,
        Rob Clark <robdclark@...omium.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Christian König 
        <ckoenig.leichtzumerken@...il.com>,
        Michel Dänzer <michel@...nzer.net>,
        open list <linux-kernel@...r.kernel.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Pekka Paalanen <ppaalanen@...il.com>,
        Luben Tuikov <luben.tuikov@....com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Alex Deucher <alexander.deucher@....com>,
        freedreno@...ts.freedesktop.org
Subject: Re: [PATCH v9 11/15] drm/atomic-helper: Set fence deadline for vblank

On Fri, Mar 03, 2023 at 07:45:05AM -0800, Rob Clark wrote:
> On Fri, Mar 3, 2023 at 7:12 AM Ville Syrjälä
> <ville.syrjala@...ux.intel.com> wrote:
> >
> > On Thu, Mar 02, 2023 at 03:53:33PM -0800, Rob Clark wrote:
> > > From: Rob Clark <robdclark@...omium.org>
> > >
> > > For an atomic commit updating a single CRTC (ie. a pageflip) calculate
> > > the next vblank time, and inform the fence(s) of that deadline.
> > >
> > > v2: Comment typo fix (danvet)
> > >
> > > Signed-off-by: Rob Clark <robdclark@...omium.org>
> > > Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
> > > Signed-off-by: Rob Clark <robdclark@...omium.org>
> > > ---
> > >  drivers/gpu/drm/drm_atomic_helper.c | 36 +++++++++++++++++++++++++++++
> > >  1 file changed, 36 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > > index d579fd8f7cb8..d8ee98ce2fc5 100644
> > > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > > @@ -1511,6 +1511,40 @@ void drm_atomic_helper_commit_modeset_enables(struct drm_device *dev,
> > >  }
> > >  EXPORT_SYMBOL(drm_atomic_helper_commit_modeset_enables);
> > >
> > > +/*
> > > + * For atomic updates which touch just a single CRTC, calculate the time of the
> > > + * next vblank, and inform all the fences of the deadline.
> > > + */
> > > +static void set_fence_deadline(struct drm_device *dev,
> > > +                            struct drm_atomic_state *state)
> > > +{
> > > +     struct drm_crtc *crtc, *wait_crtc = NULL;
> > > +     struct drm_crtc_state *new_crtc_state;
> > > +     struct drm_plane *plane;
> > > +     struct drm_plane_state *new_plane_state;
> > > +     ktime_t vbltime;
> > > +     int i;
> > > +
> > > +     for_each_new_crtc_in_state (state, crtc, new_crtc_state, i) {
> > > +             if (wait_crtc)
> > > +                     return;
> > > +             wait_crtc = crtc;
> > > +     }
> > > +
> > > +     /* If no CRTCs updated, then nothing to do: */
> > > +     if (!wait_crtc)
> > > +             return;
> >
> > Is there an actual point in limiting this to single crtc updates?
> > That immediately excludes tiled displays/etc.
> >
> > Handling an arbitrary number of crtcs shouldn't really be a lot
> > more complicated should it?
> 
> I guess I could find the soonest upcoming vblank of all the CRTCs and
> use that as the deadline?

Yeah, that seems reasonable. The flips are supposed to happen
atomically (if possible) anyway so collapsing the thing to
a single deadline for all makes sense to me.

-- 
Ville Syrjälä
Intel