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

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Message-ID: <Y/TAr64SpxO712RB@intel.com>
Date:   Tue, 21 Feb 2023 15:01:35 +0200
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Pekka Paalanen <ppaalanen@...il.com>
Cc:     Rob Clark <robdclark@...il.com>,
        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>,
        dri-devel@...ts.freedesktop.org,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Alex Deucher <alexander.deucher@....com>,
        freedreno@...ts.freedesktop.org
Subject: Re: [PATCH v4 10/14] drm/vblank: Add helper to get next vblank time

On Tue, Feb 21, 2023 at 10:45:51AM +0200, Pekka Paalanen wrote:
> On Mon, 20 Feb 2023 07:55:41 -0800
> Rob Clark <robdclark@...il.com> wrote:
> 
> > 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?
> 
> I don't know. :-)

At least for i915 this will give you the maximum frame
duration.

Also this does not calculate the the start of vblank, it
calculates the start of active video.

> 
> You need a number of clock cycles in addition to the clock frequency,
> and that could still be minimum, maximum, the last realized one, ...
> 
> VRR works by adjusting the front porch length IIRC.
> 
> 
> Thanks,
> pq
> 
> > 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,  
> > >  
> 



-- 
Ville Syrjälä
Intel