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

[Mario Kleiner]

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?

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.
> >    */
> >
> >   /**
> >
>