linux-kernel - Re: [PATCH v3 8/9] dma-buf/sync_file: Add SET

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Message-ID: <20210928105746.02304ece@eldfell>
Date:   Tue, 28 Sep 2021 10:57:46 +0300
From:   Pekka Paalanen <ppaalanen@...il.com>
To:     Rob Clark <robdclark@...il.com>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>, Daniel Vetter <daniel@...ll.ch>,
        Christian König <ckoenig.leichtzumerken@...il.com>,
        Michel Dänzer <michel@...nzer.net>,
        Rob Clark <robdclark@...omium.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Christian König <christian.koenig@....com>,
        "open list:SYNC FILE FRAMEWORK" <linux-media@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 8/9] dma-buf/sync_file: Add SET_DEADLINE ioctl

On Mon, 27 Sep 2021 07:36:05 -0700
Rob Clark <robdclark@...il.com> wrote:

> On Mon, Sep 27, 2021 at 1:42 AM Pekka Paalanen <ppaalanen@...il.com> wrote:
> >
> > On Fri,  3 Sep 2021 11:47:59 -0700
> > Rob Clark <robdclark@...il.com> wrote:
> >  
> > > From: Rob Clark <robdclark@...omium.org>
> > >
> > > The initial purpose is for igt tests, but this would also be useful for
> > > compositors that wait until close to vblank deadline to make decisions
> > > about which frame to show.
> > >
> > > Signed-off-by: Rob Clark <robdclark@...omium.org>
> > > ---
> > >  drivers/dma-buf/sync_file.c    | 19 +++++++++++++++++++
> > >  include/uapi/linux/sync_file.h | 20 ++++++++++++++++++++
> > >  2 files changed, 39 insertions(+)

...

> > > diff --git a/include/uapi/linux/sync_file.h b/include/uapi/linux/sync_file.h
> > > index ee2dcfb3d660..f67d4ffe7566 100644
> > > --- a/include/uapi/linux/sync_file.h
> > > +++ b/include/uapi/linux/sync_file.h
> > > @@ -67,6 +67,18 @@ struct sync_file_info {
> > >       __u64   sync_fence_info;
> > >  };
> > >
> > > +/**
> > > + * struct sync_set_deadline - set a deadline on a fence
> > > + * @tv_sec:  seconds elapsed since epoch
> > > + * @tv_nsec: nanoseconds elapsed since the time given by the tv_sec
> > > + * @pad:     must be zero  
> >
> > Hi Rob,
> >
> > I think you need to specify which clock this timestamp must be in.
> >
> > Which epoch? Sounds a bit like CLOCK_REALTIME to me which would not
> > make sense.  
> 
> It should be monotonic.. same clock as is used for vblank timestamps,
> which I assume that would be the most straightforward thing for
> compositors to use

Yes, it would. Just need to document that. :-)


Thanks,
pq

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