linux-kernel - Re: [RFC 01/10] [media] vb2: add explicit fence user API

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Date:   Mon, 03 Apr 2017 11:48:00 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Gustavo Padovan <gustavo@...ovan.org>
Cc:     linux-media@...r.kernel.org, Hans Verkuil <hverkuil@...all.nl>,
        Mauro Carvalho Chehab <mchehab@....samsung.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Javier Martinez Canillas <javier@....samsung.com>,
        linux-kernel@...r.kernel.org,
        Gustavo Padovan <gustavo.padovan@...labora.com>
Subject: Re: [RFC 01/10] [media] vb2: add explicit fence user API

Hi Gustavo,

On Mon, 2017-03-13 at 16:20 -0300, Gustavo Padovan wrote:
> From: Gustavo Padovan <gustavo.padovan@...labora.com>
> 
> Turn the reserved2 field into fence_fd that we will use to send
> an in-fence to the kernel return an out-fence from the kernel to
> userspace.
> 
> Two new flags were added, V4L2_BUF_FLAG_IN_FENCE and
> V4L2_BUF_FLAG_OUT_FENCE. They should be used when setting in-fence and
> out-fence, respectively.
> 
> Signed-off-by: Gustavo Padovan <gustavo.padovan@...labora.com>
> ---
>  drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 4 ++--
>  drivers/media/v4l2-core/videobuf2-v4l2.c      | 2 +-
>  include/uapi/linux/videodev2.h                | 6 ++++--
>  3 files changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> index eac9565..0a522cb 100644
> --- a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> +++ b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> @@ -348,7 +348,7 @@ struct v4l2_buffer32 {
>  		__s32		fd;
>  	} m;
>  	__u32			length;
> -	__u32			reserved2;
> +	__s32			fence_fd;
>  	__u32			reserved;
>  };
>  
> @@ -511,7 +511,7 @@ static int put_v4l2_buffer32(struct v4l2_buffer *kp, struct v4l2_buffer32 __user
>  		put_user(kp->timestamp.tv_usec, &up->timestamp.tv_usec) ||
>  		copy_to_user(&up->timecode, &kp->timecode, sizeof(struct v4l2_timecode)) ||
>  		put_user(kp->sequence, &up->sequence) ||
> -		put_user(kp->reserved2, &up->reserved2) ||
> +		put_user(kp->fence_fd, &up->fence_fd) ||
>  		put_user(kp->reserved, &up->reserved) ||
>  		put_user(kp->length, &up->length))
>  			return -EFAULT;
> diff --git a/drivers/media/v4l2-core/videobuf2-v4l2.c b/drivers/media/v4l2-core/videobuf2-v4l2.c
> index 3529849..d23c1bf 100644
> --- a/drivers/media/v4l2-core/videobuf2-v4l2.c
> +++ b/drivers/media/v4l2-core/videobuf2-v4l2.c
> @@ -203,7 +203,7 @@ static void __fill_v4l2_buffer(struct vb2_buffer *vb, void *pb)
>  	b->timestamp = ns_to_timeval(vb->timestamp);
>  	b->timecode = vbuf->timecode;
>  	b->sequence = vbuf->sequence;
> -	b->reserved2 = 0;
> +	b->fence_fd = -1;
>  	b->reserved = 0;
>  
>  	if (q->is_multiplanar) {
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 45184a2..3b6cfa6 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -911,7 +911,7 @@ struct v4l2_buffer {
>  		__s32		fd;
>  	} m;
>  	__u32			length;
> -	__u32			reserved2;
> +	__s32			fence_fd;
>  	__u32			reserved;
>  };
>  
> @@ -946,8 +946,10 @@ struct v4l2_buffer {
>  #define V4L2_BUF_FLAG_TSTAMP_SRC_MASK		0x00070000
>  #define V4L2_BUF_FLAG_TSTAMP_SRC_EOF		0x00000000
>  #define V4L2_BUF_FLAG_TSTAMP_SRC_SOE		0x00010000
> +#define V4L2_BUF_FLAG_IN_FENCE			0x00100000
> +#define V4L2_BUF_FLAG_OUT_FENCE			0x00200000
>  /* mem2mem encoder/decoder */
> -#define V4L2_BUF_FLAG_LAST			0x00100000
> +#define V4L2_BUF_FLAG_LAST			0x00400000

This is not just a sentinel, it is a meaningful flag that must not be
changed. It indicates the last buffer produced by a hardware codec.

regards
Philipp