linux-kernel - Re: [PATCH v4 05/14] dma-buf/sync_file: Add SET

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Date:   Mon, 20 Feb 2023 08:09:04 -0800
From:   Rob Clark <robdclark@...il.com>
To:     Christian König <christian.koenig@....com>
Cc:     dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        Daniel Vetter <daniel@...ll.ch>,
        Christian König <ckoenig.leichtzumerken@...il.com>,
        Michel Dänzer <michel@...nzer.net>,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Alex Deucher <alexander.deucher@....com>,
        Pekka Paalanen <ppaalanen@...il.com>,
        Simon Ser <contact@...rsion.fr>,
        Rob Clark <robdclark@...omium.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Gustavo Padovan <gustavo@...ovan.org>,
        "open list:SYNC FILE FRAMEWORK" <linux-media@...r.kernel.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 05/14] dma-buf/sync_file: Add SET_DEADLINE ioctl

On Mon, Feb 20, 2023 at 12:27 AM Christian König
<christian.koenig@....com> wrote:
>
> Am 18.02.23 um 22:15 schrieb Rob Clark:
> > 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.
> >
> > The igt tests can be found at:
> >
> > https://gitlab.freedesktop.org/robclark/igt-gpu-tools/-/commits/fence-deadline
> >
> > v2: Clarify the timebase, add link to igt tests
> >
> > Signed-off-by: Rob Clark <robdclark@...omium.org>
> > ---
> >   drivers/dma-buf/sync_file.c    | 19 +++++++++++++++++++
> >   include/uapi/linux/sync_file.h | 22 ++++++++++++++++++++++
> >   2 files changed, 41 insertions(+)
> >
> > diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
> > index af57799c86ce..fb6ca1032885 100644
> > --- a/drivers/dma-buf/sync_file.c
> > +++ b/drivers/dma-buf/sync_file.c
> > @@ -350,6 +350,22 @@ 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)
> >   {
> > @@ -362,6 +378,9 @@ 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..c8666580816f 100644
> > --- a/include/uapi/linux/sync_file.h
> > +++ b/include/uapi/linux/sync_file.h
> > @@ -67,6 +67,20 @@ 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
> > + *
> > + * The timebase for the deadline is CLOCK_MONOTONIC (same as vblank)
> > + */
> > +struct sync_set_deadline {
> > +     __s64   tv_sec;
> > +     __s32   tv_nsec;
> > +     __u32   pad;
>
> IIRC struct timespec defined this as time_t/long (which is horrible for
> an UAPI because of the sizeof(long) dependency), one possible
> alternative is to use 64bit nanoseconds from CLOCK_MONOTONIC (which is
> essentially ktime).
>
> Not 100% sure if there is any preferences documented, but I think the
> later might be better.

The original thought is that this maps directly to clock_gettime()
without extra conversion needed, and is similar to other pre-ktime_t
UAPI.  But OTOH if userspace wants to add an offset, it is maybe
better to convert completely to ns in userspace and use a u64 (as that
is what ns_to_ktime() uses).. (and OFC whatever decision here also
applies to the syncobj wait ioctls)

I'm leaning towards u64 CLOCK_MONOTONIC ns if no one has a good
argument against that.

BR,
-R

> Either way the patch is Acked-by: Christian König
> <christian.koenig@....com> for this patch.
>
> Regards,
> Christian.
>
> > +};
> > +
> >   #define SYNC_IOC_MAGIC              '>'
> >
> >   /**
> > @@ -95,4 +109,12 @@ 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 */
>