[RFC][PATCH 05/15] videobuf2: handle V4L2_FLAG_MEMORY_NON_CONSISTENT in REQBUFS

[Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>]

This patch lets user-space to request a non-consistent memory
allocation during REQBUFS ioctl call. We use one bit of a
->reserved[1] member of struct v4l2_requestbuffers, which is
now renamed to ->flags.

There is just 1 four-byte reserved area in v4l2_requestbuffers
struct, therefore for backward compatibility ->reserved and
->flags were put into anonymous union.

Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
---
 Documentation/media/uapi/v4l/vidioc-reqbufs.rst | 14 ++++++++++++--
 drivers/media/common/videobuf2/videobuf2-v4l2.c | 14 ++++++++++++--
 drivers/media/v4l2-core/v4l2-ioctl.c            |  3 ---
 include/uapi/linux/videodev2.h                  |  5 ++++-
 4 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/Documentation/media/uapi/v4l/vidioc-reqbufs.rst b/Documentation/media/uapi/v4l/vidioc-reqbufs.rst
index d0c643db477a..9b69a61d9fd4 100644
--- a/Documentation/media/uapi/v4l/vidioc-reqbufs.rst
+++ b/Documentation/media/uapi/v4l/vidioc-reqbufs.rst
@@ -112,10 +112,20 @@ aborting or finishing any DMA in progress, an implicit
 	``V4L2_MEMORY_MMAP`` and ``type`` set to the buffer type. This will
 	free any previously allocated buffers, so this is typically something
 	that will be done at the start of the application.
-    * - __u32
+    * - union
+      - (anonymous)
+    * -
+      - __u32
+      - ``flags``\ [1]
+      - Specifies additional buffer management attributes. E.g. when
+        ``V4L2_FLAG_MEMORY_NON_CONSISTENT`` set vb2 backends may be allocated
+        in non-consistent memory.
+    * -
+      - __u32
       - ``reserved``\ [1]
       - A place holder for future extensions. Drivers and applications
-	must set the array to zero.
+	must set the array to zero, unless application wants to specify
+        buffer management ``flags``.
 
 .. tabularcolumns:: |p{6.1cm}|p{2.2cm}|p{8.7cm}|
 
diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
index f1e88c9398c7..0eabb589684f 100644
--- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
+++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
@@ -693,9 +693,15 @@ static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
 int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
 {
 	int ret = vb2_verify_memory_type(q, req->memory, req->type);
+	bool consistent = true;
+
+	if (req->flags & V4L2_FLAG_MEMORY_NON_CONSISTENT)
+		consistent = false;
 
 	fill_buf_caps(q, &req->capabilities);
-	return ret ? ret : vb2_core_reqbufs(q, req->memory, true, &req->count);
+	if (ret)
+		return ret;
+	return vb2_core_reqbufs(q, req->memory, consistent, &req->count);
 }
 EXPORT_SYMBOL_GPL(vb2_reqbufs);
 
@@ -939,13 +945,17 @@ int vb2_ioctl_reqbufs(struct file *file, void *priv,
 {
 	struct video_device *vdev = video_devdata(file);
 	int res = vb2_verify_memory_type(vdev->queue, p->memory, p->type);
+	bool consistent = true;
 
 	fill_buf_caps(vdev->queue, &p->capabilities);
 	if (res)
 		return res;
 	if (vb2_queue_is_busy(vdev, file))
 		return -EBUSY;
-	res = vb2_core_reqbufs(vdev->queue, p->memory, true, &p->count);
+	if (p->flags & V4L2_FLAG_MEMORY_NON_CONSISTENT)
+		consistent = false;
+
+	res = vb2_core_reqbufs(vdev->queue, p->memory, consistent, &p->count);
 	/* If count == 0, then the owner has released all buffers and he
 	   is no longer owner of the queue. Otherwise we have a new owner. */
 	if (res == 0)
diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
index 003b7422aeef..225d06819bce 100644
--- a/drivers/media/v4l2-core/v4l2-ioctl.c
+++ b/drivers/media/v4l2-core/v4l2-ioctl.c
@@ -1973,9 +1973,6 @@ static int v4l_reqbufs(const struct v4l2_ioctl_ops *ops,
 
 	if (ret)
 		return ret;
-
-	CLEAR_AFTER_FIELD(p, capabilities);
-
 	return ops->vidioc_reqbufs(file, fh, p);
 }
 
diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
index d352997f2b62..73a4854f71bd 100644
--- a/include/uapi/linux/videodev2.h
+++ b/include/uapi/linux/videodev2.h
@@ -919,7 +919,10 @@ struct v4l2_requestbuffers {
 	__u32			type;		/* enum v4l2_buf_type */
 	__u32			memory;		/* enum v4l2_memory */
 	__u32			capabilities;
-	__u32			reserved[1];
+	union {
+		__u32		flags;
+		__u32		reserved[1];
+	};
 };
 
 /* capabilities for struct v4l2_requestbuffers and v4l2_create_buffers */
-- 
2.24.1.735.g03f4e72817-goog