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

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Date:   Mon, 20 Feb 2023 09:27:47 +0100
From:   Christian König <christian.koenig@....com>
To:     Rob Clark <robdclark@...il.com>, dri-devel@...ts.freedesktop.org
Cc:     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

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.

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 */