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

[Pekka Paalanen <ppaalanen@gmail.com>]

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On Fri,  3 Sep 2021 11:47:59 -0700
Rob Clark <robdclark@gmail.com> wrote:

> From: Rob Clark <robdclark@chromium.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@chromium.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.

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 */


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