Re: [PATCH v4 05/14] dma-buf/sync_file: Add SET_DEADLINE ioctl

[Christian König]

Am 20.02.23 um 17:09 schrieb Rob Clark:
> On Mon, Feb 20, 2023 at 12:27 AM Christian König
> <christian.koenig@xxxxxxx> wrote:
> > Am 18.02.23 um 22:15 schrieb Rob Clark:
> > > From: Rob Clark <robdclark@xxxxxxxxxxxx>
> > >
> > > 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@xxxxxxxxxxxx>
> > > ---
> > >    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.

+1 for that.

Regards,
Christian.

> BR,
> -R
>
> > Either way the patch is Acked-by: Christian König
> > <christian.koenig@xxxxxxx> 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 */