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Subject[PATCH v9 10/15] vb2: add explicit fence user API
Date
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 or 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 an in-fence to the kernel to be waited on, and
V4L2_BUF_FLAG_OUT_FENCE, to ask the kernel to give back an out-fence.

v7: minor fixes on the Documentation (Hans Verkuil)

v6: big improvement on doc (Hans Verkuil)

v5: - keep using reserved2 field for cpia2
- set fence_fd to 0 for now, for compat with userspace(Mauro)

v4: make it a union with reserved2 and fence_fd (Hans Verkuil)

v3: make the out_fence refer to the current buffer (Hans Verkuil)

v2: add documentation

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
---
Documentation/media/uapi/v4l/buffer.rst | 45 +++++++++++++++++++++++--
drivers/media/common/videobuf2/videobuf2-v4l2.c | 2 +-
drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 4 +--
include/uapi/linux/videodev2.h | 8 ++++-
4 files changed, 52 insertions(+), 7 deletions(-)

diff --git a/Documentation/media/uapi/v4l/buffer.rst b/Documentation/media/uapi/v4l/buffer.rst
index e2c85ddc990b..be9719cf5745 100644
--- a/Documentation/media/uapi/v4l/buffer.rst
+++ b/Documentation/media/uapi/v4l/buffer.rst
@@ -301,10 +301,22 @@ struct v4l2_buffer
elements in the ``planes`` array. The driver will fill in the
actual number of valid elements in that array.
* - __u32
- - ``reserved2``
+ - ``fence_fd``
-
- - A place holder for future extensions. Drivers and applications
- must set this to 0.
+ - Used to communicate a fence file descriptors from userspace to kernel
+ and vice-versa. On :ref:`VIDIOC_QBUF <VIDIOC_QBUF>` when sending
+ an in-fence for V4L2 to wait on, the ``V4L2_BUF_FLAG_IN_FENCE`` flag must
+ be used and this field set to the fence file descriptor of the in-fence.
+ If the in-fence is not valid ` VIDIOC_QBUF`` returns an error.
+
+ To get an out-fence back from V4L2 the ``V4L2_BUF_FLAG_OUT_FENCE``
+ must be set, the kernel will return the out-fence file descriptor in
+ this field. If it fails to create the out-fence ``VIDIOC_QBUF` returns
+ an error.
+
+ For all other ioctls V4L2 sets this field to -1 if
+ ``V4L2_BUF_FLAG_IN_FENCE`` and/or ``V4L2_BUF_FLAG_OUT_FENCE`` are set,
+ otherwise this field is set to 0 for backward compatibility.
* - __u32
- ``reserved``
-
@@ -648,6 +660,33 @@ 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 the fence passed in the ``fence_fd`` field. The
+ buffer won't be queued to the driver until the fence signals. The order
+ in which buffers are queued is guaranteed to be preserved, so any
+ buffers queued after this buffer will also be blocked until this fence
+ signals. This flag must be set before calling ``VIDIOC_QBUF``. For
+ other ioctls the driver just reports the value of the flag.
+
+ If the fence signals the flag is cleared and not reported anymore.
+ If the fence is not valid ``VIDIOC_QBUF`` returns an error.
+
+
+ * .. _`V4L2-BUF-FLAG-OUT-FENCE`:
+
+ - ``V4L2_BUF_FLAG_OUT_FENCE``
+ - 0x00400000
+ - Request for a fence to be attached to the buffer. The driver will fill
+ in the out-fence fd in the ``fence_fd`` field when :ref:`VIDIOC_QBUF
+ <VIDIOC_QBUF>` returns. This flag must be set before calling
+ ``VIDIOC_QBUF``. For other ioctls the driver just reports the value of
+ the flag.
+
+ If the creation of the out-fence fails ``VIDIOC_QBUF`` returns an
+ error.



diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
index 64503615d00b..b1c0fa2b0b88 100644
--- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
+++ b/drivers/media/common/videobuf2/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 = 0;
b->reserved = 0;

if (q->is_multiplanar) {
diff --git a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
index 4312935f1dfc..93c752459aec 100644
--- a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
+++ b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
@@ -388,7 +388,7 @@ struct v4l2_buffer32 {
__s32 fd;
} m;
__u32 length;
- __u32 reserved2;
+ __s32 fence_fd;
__u32 reserved;
};

@@ -606,7 +606,7 @@ static int put_v4l2_buffer32(struct v4l2_buffer __user *kp,
assign_in_user(&up->timestamp.tv_usec, &kp->timestamp.tv_usec) ||
copy_in_user(&up->timecode, &kp->timecode, sizeof(kp->timecode)) ||
assign_in_user(&up->sequence, &kp->sequence) ||
- assign_in_user(&up->reserved2, &kp->reserved2) ||
+ assign_in_user(&up->fence_fd, &kp->fence_fd) ||
assign_in_user(&up->reserved, &kp->reserved) ||
get_user(length, &kp->length) ||
put_user(length, &up->length))
diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
index a8842a5ca636..1f18dc68ecab 100644
--- a/include/uapi/linux/videodev2.h
+++ b/include/uapi/linux/videodev2.h
@@ -934,7 +934,10 @@ struct v4l2_buffer {
__s32 fd;
} m;
__u32 length;
- __u32 reserved2;
+ union {
+ __s32 fence_fd;
+ __u32 reserved2;
+ };
__u32 reserved;
};

@@ -971,6 +974,9 @@ struct v4l2_buffer {
#define V4L2_BUF_FLAG_TSTAMP_SRC_SOE 0x00010000
/* mem2mem encoder/decoder */
#define V4L2_BUF_FLAG_LAST 0x00100000
+/* Explicit synchronization */
+#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
--
2.16.3
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