linux-kernel - Re: [PATCH v4 10/14] drm/vblank: Add helper to get next vblank time

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Message-ID: <CAF6AEGuo-vmW4Va9=RH+kH9KgNvR2vzjJ8meO-oty56xjDhjgg@mail.gmail.com>
Date:   Mon, 20 Feb 2023 07:55:41 -0800
From:   Rob Clark <robdclark@...il.com>
To:     Pekka Paalanen <ppaalanen@...il.com>
Cc:     dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        Daniel Vetter <daniel@...ll.ch>,
        Christian König <ckoenig.leichtzumerken@...il.com>,
        Michel Dänzer <michel@...nzer.net>,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Alex Deucher <alexander.deucher@....com>,
        Simon Ser <contact@...rsion.fr>,
        Rob Clark <robdclark@...omium.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 10/14] drm/vblank: Add helper to get next vblank time

On Mon, Feb 20, 2023 at 1:08 AM Pekka Paalanen <ppaalanen@...il.com> wrote:
>
> On Sat, 18 Feb 2023 13:15:53 -0800
> Rob Clark <robdclark@...il.com> wrote:
>
> > From: Rob Clark <robdclark@...omium.org>
> >
> > Will be used in the next commit to set a deadline on fences that an
> > atomic update is waiting on.
> >
> > Signed-off-by: Rob Clark <robdclark@...omium.org>
> > ---
> >  drivers/gpu/drm/drm_vblank.c | 32 ++++++++++++++++++++++++++++++++
> >  include/drm/drm_vblank.h     |  1 +
> >  2 files changed, 33 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> > index 2ff31717a3de..caf25ebb34c5 100644
> > --- a/drivers/gpu/drm/drm_vblank.c
> > +++ b/drivers/gpu/drm/drm_vblank.c
> > @@ -980,6 +980,38 @@ u64 drm_crtc_vblank_count_and_time(struct drm_crtc *crtc,
> >  }
> >  EXPORT_SYMBOL(drm_crtc_vblank_count_and_time);
> >
> > +/**
> > + * drm_crtc_next_vblank_time - calculate the time of the next vblank
> > + * @crtc: the crtc for which to calculate next vblank time
> > + * @vblanktime: pointer to time to receive the next vblank timestamp.
> > + *
> > + * Calculate the expected time of the next vblank based on time of previous
> > + * vblank and frame duration
>
> Hi,
>
> for VRR this targets the highest frame rate possible for the current
> VRR mode, right?
>

It is based on vblank->framedur_ns which is in turn based on
mode->crtc_clock.  Presumably for VRR that ends up being a maximum?

BR,
-R


>
> Thanks,
> pq
>
> > + */
> > +int drm_crtc_next_vblank_time(struct drm_crtc *crtc, ktime_t *vblanktime)
> > +{
> > +     unsigned int pipe = drm_crtc_index(crtc);
> > +     struct drm_vblank_crtc *vblank = &crtc->dev->vblank[pipe];
> > +     u64 count;
> > +
> > +     if (!vblank->framedur_ns)
> > +             return -EINVAL;
> > +
> > +     count = drm_vblank_count_and_time(crtc->dev, pipe, vblanktime);
> > +
> > +     /*
> > +      * If we don't get a valid count, then we probably also don't
> > +      * have a valid time:
> > +      */
> > +     if (!count)
> > +             return -EINVAL;
> > +
> > +     *vblanktime = ktime_add(*vblanktime, ns_to_ktime(vblank->framedur_ns));
> > +
> > +     return 0;
> > +}
> > +EXPORT_SYMBOL(drm_crtc_next_vblank_time);
> > +
> >  static void send_vblank_event(struct drm_device *dev,
> >               struct drm_pending_vblank_event *e,
> >               u64 seq, ktime_t now)
> > diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
> > index 733a3e2d1d10..a63bc2c92f3c 100644
> > --- a/include/drm/drm_vblank.h
> > +++ b/include/drm/drm_vblank.h
> > @@ -230,6 +230,7 @@ bool drm_dev_has_vblank(const struct drm_device *dev);
> >  u64 drm_crtc_vblank_count(struct drm_crtc *crtc);
> >  u64 drm_crtc_vblank_count_and_time(struct drm_crtc *crtc,
> >                                  ktime_t *vblanktime);
> > +int drm_crtc_next_vblank_time(struct drm_crtc *crtc, ktime_t *vblanktime);
> >  void drm_crtc_send_vblank_event(struct drm_crtc *crtc,
> >                              struct drm_pending_vblank_event *e);
> >  void drm_crtc_arm_vblank_event(struct drm_crtc *crtc,
>