[PATCH] drm: Fix timestamp docs for variable refresh properties.

[Alex Deucher]

On Tue, May 7, 2019 at 1:15 AM Mario Kleiner <mario.kleiner.de at gmail.com> wrote:
>
> Nag nag: The below documentation patch, acked-by Daniel and r-b'd by
> Nicholas seems to not have made it into drm-next yet?

Pushed to drm-misc-next-fixes

Thanks!

Alex

>
> thanks,
> -mario
>
> On Thu, Apr 18, 2019 at 2:45 PM Kazlauskas, Nicholas
> <Nicholas.Kazlauskas at amd.com> wrote:
> >
> > On 4/18/19 2:01 AM, Mario Kleiner wrote:
> > > As discussed with Nicholas and Daniel Vetter (patchwork
> > > link to discussion below), the VRR timestamping behaviour
> > > produced utterly useless and bogus vblank/pageflip
> > > timestamps. We have found a way to fix this and provide
> > > sane behaviour.
> > >
> > > As of Linux 5.2, the amdgpu driver will be able to
> > > provide exactly the same vblank / pageflip timestamp
> > > semantic in variable refresh rate mode as in standard
> > > fixed refresh rate mode. This is achieved by deferring
> > > core vblank handling (drm_crtc_handle_vblank()) until
> > > the end of front porch, and also defer the sending of
> > > pageflip completion events until end of front porch,
> > > when we can safely compute correct pageflip/vblank
> > > timestamps.
> > >
> > > The same approach will be possible for other VRR
> > > capable kms drivers, so we can actually have sane
> > > and useful timestamps in VRR mode.
> > >
> > > This patch removes the section of the docs that
> > > describes the broken timestamp behaviour present
> > > in Linux 5.0/5.1.
> > >
> > > Fixes: ab7a664f7a2d ("drm: Document variable refresh properties")
> > > Link: https://patchwork.freedesktop.org/patch/285333/
> > > Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
> >
> > Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>
> >
> > Someone else can feel free to push this as I don't have commit rights
> > for DRM.
> >
> > Thanks!
> >
> > Nicholas Kazlauskas
> >
> > > ---
> > >   drivers/gpu/drm/drm_connector.c | 6 ------
> > >   1 file changed, 6 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> > > index 2355124849db..b34c3d38bf15 100644
> > > --- a/drivers/gpu/drm/drm_connector.c
> > > +++ b/drivers/gpu/drm/drm_connector.c
> > > @@ -1416,12 +1416,6 @@ EXPORT_SYMBOL(drm_mode_create_scaling_mode_property);
> > >    *
> > >    *  The driver may place further restrictions within these minimum
> > >    *  and maximum bounds.
> > > - *
> > > - *   The semantics for the vertical blank timestamp differ when
> > > - *   variable refresh rate is active. The vertical blank timestamp
> > > - *   is defined to be an estimate using the current mode's fixed
> > > - *   refresh rate timings. The semantics for the page-flip event
> > > - *   timestamp remain the same.
> > >    */
> > >
> > >   /**
> > >
> >
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