Re: [PATCH v3 8/9] dma-buf/sync_file: Add SET_DEADLINE ioctl

[Christian König]

Am 27.09.21 um 10:42 schrieb Pekka Paalanen:
> On Fri,  3 Sep 2021 11:47:59 -0700
> Rob Clark <robdclark@xxxxxxxxx> wrote:
>
> > 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.
> >
> > Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
> > ---
> >   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.

Most likely CLOCK_MONOTONIC I think since that's what ktime is based on 
as well IIRC.

My recollection might be wrong but I think Daniel documented somewhere 
that an absolut 64bit nanosecond value should be used for timeouts in 
IOCTLs which is sufficient for ~500 years uptime.

So the separation between seconds and nanoseconds might be redundant.

Regards,
Christian.

> 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 */