On Wed, Feb 22, 2023 at 07:44:42AM -0800, Rob Clark wrote: > On Wed, Feb 22, 2023 at 1:57 AM Pekka Paalanen <ppaalanen@xxxxxxxxx> wrote: > > > > On Tue, 21 Feb 2023 09:50:20 -0800 > > Rob Clark <robdclark@xxxxxxxxx> wrote: > > > > > On Tue, Feb 21, 2023 at 5:01 AM Ville Syrjälä > > > <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > > > > > > > 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@xxxxxxxxx> wrote: > > > > > > > > > > > On Mon, Feb 20, 2023 at 1:08 AM Pekka Paalanen <ppaalanen@xxxxxxxxx> wrote: > > > > > > > > > > > > > > On Sat, 18 Feb 2023 13:15:53 -0800 > > > > > > > Rob Clark <robdclark@xxxxxxxxx> wrote: > > > > > > > > > > > > > > > From: Rob Clark <robdclark@xxxxxxxxxxxx> > > > > > > > > > > > > > > > > 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@xxxxxxxxxxxx> > > > > > > > > --- > > > > > > > > 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. > > > > > > I suppose one could argue that maximum frame duration is the actual > > > deadline. Anything less is just moar fps, but not going to involve > > > stalling until vblank N+1, AFAIU > > > > > > > Also this does not calculate the the start of vblank, it > > > > calculates the start of active video. > > > > > > Probably something like end of previous frame's video.. might not be > > > _exactly_ correct (because some buffering involved), but OTOH on the > > > GPU side, I expect the driver to set a timer for a few ms or so before > > > the deadline. So there is some wiggle room. > > > > The vblank timestamp is defined to be the time of the first active > > pixel of the frame in the video signal. At least that's the one that > > UAPI carries (when not tearing?). It is not the start of vblank period. > > > > With VRR, the front porch before the first active pixel can be multiple > > milliseconds. The difference between 144 Hz and 60 Hz is 9.7 ms for > > example. > > What we really want is the deadline for the hw to latch for the next > frame.. which as Ville pointed out is definitely before the end of > vblank. > > Honestly this sort of feature is a lot more critical for the non-VRR > case, and VRR is kind of a minority edge case. So I'd prefer not to > get too hung up on VRR. If there is an easy way for the helpers to > detect VRR, I'd be perfectly fine not setting a deadline hint in that > case, and let someone who actually has a VRR display figure out how to > handle that case. The formula I gave you earlier works for both VRR and non-VRR. -- Ville Syrjälä Intel
