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

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Message-ID: <CAF6AEGudjfgN+x_KxyED+1XBod7yNqLN43or7vs8h7UKQmzK7Q@mail.gmail.com>
Date:   Mon, 27 Sep 2021 07:36:05 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Pekka Paalanen <ppaalanen@...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, 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/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
> > index 394e6e1e9686..f295772d5169 100644
> > --- a/drivers/dma-buf/sync_file.c
> > +++ b/drivers/dma-buf/sync_file.c
> > @@ -459,6 +459,22 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
> >       return ret;
> >  }
> >
> > +static int sync_file_ioctl_set_deadline(struct sync_file *sync_file,
> > +                                     unsigned long arg)
> > +{
> > +     struct sync_set_deadline ts;
> > +
> > +     if (copy_from_user(&ts, (void __user *)arg, sizeof(ts)))
> > +             return -EFAULT;
> > +
> > +     if (ts.pad)
> > +             return -EINVAL;
> > +
> > +     dma_fence_set_deadline(sync_file->fence, ktime_set(ts.tv_sec, ts.tv_nsec));
> > +
> > +     return 0;
> > +}
> > +
> >  static long sync_file_ioctl(struct file *file, unsigned int cmd,
> >                           unsigned long arg)
> >  {
> > @@ -471,6 +487,9 @@ static long sync_file_ioctl(struct file *file, unsigned int cmd,
> >       case SYNC_IOC_FILE_INFO:
> >               return sync_file_ioctl_fence_info(sync_file, arg);
> >
> > +     case SYNC_IOC_SET_DEADLINE:
> > +             return sync_file_ioctl_set_deadline(sync_file, arg);
> > +
> >       default:
> >               return -ENOTTY;
> >       }
> > 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

BR,
-R

> Also I cannot guess how a compositor should be using this, so
> explaining the expected usage would be really good, with reasons for
> why should userspace bother.
>
>
> Thanks,
> pq
>
> > + */
> > +struct sync_set_deadline {
> > +     __s64   tv_sec;
> > +     __s32   tv_nsec;
> > +     __u32   pad;
> > +};
> > +
> >  #define SYNC_IOC_MAGIC               '>'
> >
> >  /**
> > @@ -95,4 +107,12 @@ struct sync_file_info {
> >   */
> >  #define SYNC_IOC_FILE_INFO   _IOWR(SYNC_IOC_MAGIC, 4, struct sync_file_info)
> >
> > +
> > +/**
> > + * DOC: SYNC_IOC_SET_DEADLINE - set a deadline on a fence
> > + *
> > + * Allows userspace to set a deadline on a fence, see dma_fence_set_deadline()
> > + */
> > +#define SYNC_IOC_SET_DEADLINE        _IOW(SYNC_IOC_MAGIC, 5, struct sync_set_deadline)
> > +
> >  #endif /* _UAPI_LINUX_SYNC_H */
>