Re: [PATCH v3 02/15] [media] vb2: add explicit fence user API

[Brian Starkey <brian.starkey@arm.com>]

Hi,

On Thu, Sep 07, 2017 at 03:42:13PM -0300, Gustavo Padovan wrote:
>From: Gustavo Padovan <gustavo.padovan@collabora.com>
>
>Turn the reserved2 field into fence_fd that we will use to send
>an in-fence to the kernel and return an out-fence from the kernel to
>userspace.
>
>Two new flags were added, V4L2_BUF_FLAG_IN_FENCE, that should be used
>when sending a fence to the kernel to be waited on, and
>V4L2_BUF_FLAG_OUT_FENCE, to ask the kernel to give back an out-fence.

It seems a bit off to me to add this to the uapi, and document it,
before any of the implementation is present in the kernel.

Wouldn't it be better to move this patch to be the last one, after all
of the implementation is done?

Cheers,
-Brian

>
>v2: add documentation
>
>Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
>---
> Documentation/media/uapi/v4l/buffer.rst       | 19 +++++++++++++++++++
> drivers/media/usb/cpia2/cpia2_v4l.c           |  2 +-
> drivers/media/v4l2-core/v4l2-compat-ioctl32.c |  4 ++--
> drivers/media/v4l2-core/videobuf2-v4l2.c      |  2 +-
> include/uapi/linux/videodev2.h                |  4 +++-
> 5 files changed, 26 insertions(+), 5 deletions(-)
>
>diff --git a/Documentation/media/uapi/v4l/buffer.rst b/Documentation/media/uapi/v4l/buffer.rst
>index ae6ee73f151c..664507ad06c6 100644
>--- a/Documentation/media/uapi/v4l/buffer.rst
>+++ b/Documentation/media/uapi/v4l/buffer.rst
>@@ -648,6 +648,25 @@ Buffer Flags
>       - Start Of Exposure. The buffer timestamp has been taken when the
> 	exposure of the frame has begun. This is only valid for the
> 	``V4L2_BUF_TYPE_VIDEO_CAPTURE`` buffer type.
>+    * .. _`V4L2-BUF-FLAG-IN-FENCE`:
>+
>+      - ``V4L2_BUF_FLAG_IN_FENCE``
>+      - 0x00200000
>+      - Ask V4L2 to wait on fence passed in ``fence_fd`` field. The buffer
>+	won't be queued to the driver until the fence signals.
>+
>+    * .. _`V4L2-BUF-FLAG-OUT-FENCE`:
>+
>+      - ``V4L2_BUF_FLAG_OUT_FENCE``
>+      - 0x00400000
>+      - Request a fence for the next buffer to be queued to V4L2 driver.
>+	The fence received back through the ``fence_fd`` field  doesn't
>+	necessarily relate to the current buffer in the
>+	:ref:`VIDIOC_QBUF <VIDIOC_QBUF>` ioctl. Although, most of the time
>+	the fence will relate to the current buffer it can't be guaranteed.
>+	So to tell userspace which buffer is associated to the out_fence,
>+	one should listen for the ``V4L2_EVENT_BUF_QUEUED`` event that
>+	provide the id of the buffer when it is queued to the V4L2 driver.
>
>
>
>diff --git a/drivers/media/usb/cpia2/cpia2_v4l.c b/drivers/media/usb/cpia2/cpia2_v4l.c
>index 3dedd83f0b19..6cde686bf44c 100644
>--- a/drivers/media/usb/cpia2/cpia2_v4l.c
>+++ b/drivers/media/usb/cpia2/cpia2_v4l.c
>@@ -948,7 +948,7 @@ static int cpia2_dqbuf(struct file *file, void *fh, struct v4l2_buffer *buf)
> 	buf->sequence = cam->buffers[buf->index].seq;
> 	buf->m.offset = cam->buffers[buf->index].data - cam->frame_buffer;
> 	buf->length = cam->frame_size;
>-	buf->reserved2 = 0;
>+	buf->fence_fd = -1;
> 	buf->reserved = 0;
> 	memset(&buf->timecode, 0, sizeof(buf->timecode));
>
>diff --git a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
>index 821f2aa299ae..d624fb5df130 100644
>--- a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
>+++ b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
>@@ -370,7 +370,7 @@ struct v4l2_buffer32 {
> 		__s32		fd;
> 	} m;
> 	__u32			length;
>-	__u32			reserved2;
>+	__s32			fence_fd;
> 	__u32			reserved;
> };
>
>@@ -533,8 +533,8 @@ 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->reserved, &up->reserved) ||
>+		put_user(kp->fence_fd, &up->fence_fd) ||
> 		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 0c0669976bdc..110fb45fef6f 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 185d6a0acc06..e5abab9a908c 100644
>--- a/include/uapi/linux/videodev2.h
>+++ b/include/uapi/linux/videodev2.h
>@@ -924,7 +924,7 @@ struct v4l2_buffer {
> 		__s32		fd;
> 	} m;
> 	__u32			length;
>-	__u32			reserved2;
>+	__s32			fence_fd;
> 	__u32			reserved;
> };
>
>@@ -961,6 +961,8 @@ struct v4l2_buffer {
> #define V4L2_BUF_FLAG_TSTAMP_SRC_SOE		0x00010000
> /* mem2mem encoder/decoder */
> #define V4L2_BUF_FLAG_LAST			0x00100000
>+#define V4L2_BUF_FLAG_IN_FENCE			0x00200000
>+#define V4L2_BUF_FLAG_OUT_FENCE			0x00400000
>
> /**
>  * struct v4l2_exportbuffer - export of video buffer as DMABUF file descriptor
>-- 
>2.13.5
>