On Fri, Dec 3, 2021 at 1:03 PM Michel Dänzer <[email protected]> wrote:
>
> On 2021-12-03 16:58, Matthias Brugger wrote:
> > Hi Mark,
> >
> > On 02/12/2021 16:11, Mark Yacoub wrote:
> >> From: Mark Yacoub <[email protected]>
> >>
> >
> > please make sure to add the linux-mediatek mailinglist in any follow-up
> > communication.
> >
> > Regards,
> > Matthias
> >
> >> [Why]
> >> drm_handle_vblank_events loops over vblank_event_list to send any event
> >> that is current or has passed.
> >> More than 1 event could be pending with past sequence time that need to
> >> be send. This can be a side effect of drivers without hardware vblank
> >> counter and they depend on the difference in the timestamps and the
> >> frame/field duration calculated in drm_update_vblank_count. This can
> >> lead to 1 vblirq being ignored due to very small diff,
>
> That sounds like the real issue which needs to be addressed. As Ville wrote,
> the sequence value in the event is supposed to be the current sequence, not
> the one which was specified originally by user space. So this change would
> basically break the universe. ;)
>
I don't wanna be the reason to break the universe :)) I guess I
misunderstood what the call does, will look into the real issue more.
Thanks everyone!
>
> >> resulting in a subsequent vblank with 2 pending vblank events to be sent,
> >> each with a
> >> unique sequence expected by user space.
> >>
> >> [How]
> >> Send each pending vblank event with the sequence it's waiting on instead
> >> of assigning the current sequence to all of them.
> >>
> >> Fixes igt@kms_flip "Unexpected frame sequence"
> >> Tested on Jacuzzi (MT8183)
> >>
> >> Signed-off-by: Mark Yacoub <[email protected]>
> >> ---
> >> drivers/gpu/drm/drm_vblank.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> >> index 3417e1ac79185..47da8056abc14 100644
> >> --- a/drivers/gpu/drm/drm_vblank.c
> >> +++ b/drivers/gpu/drm/drm_vblank.c
> >> @@ -1902,7 +1902,7 @@ static void drm_handle_vblank_events(struct
> >> drm_device *dev, unsigned int pipe)
> >> list_del(&e->base.link);
> >> drm_vblank_put(dev, pipe);
> >> - send_vblank_event(dev, e, seq, now);
> >> + send_vblank_event(dev, e, e->sequence, now);
> >> }
> >> if (crtc && crtc->funcs->get_vblank_timestamp)
> >>
>
>
>
> --
> Earthling Michel Dänzer | https://redhat.com
> Libre software enthusiast | Mesa and Xwayland developer
