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* [RFCv2 PATCH] vb2: add V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF
@ 2019-05-15 12:32 Hans Verkuil
  2019-05-15 17:01 ` Boris Brezillon
  0 siblings, 1 reply; 2+ messages in thread
From: Hans Verkuil @ 2019-05-15 12:32 UTC (permalink / raw)
  To: Linux Media Mailing List, Tomasz Figa, Paul Kocialkowski,
	Alexandre Courbot, Nicolas Dufresne, Boris Brezillon,
	Thierry Reding, Maxime Ripard

This RFC patch adds support for the V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF flag.
It also adds a new V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF capability and
a v4l2_m2m_release_capture_buf() helper function.

Drivers should set vb2_queue->subsystem_flags to VB2_V4L2_FL_SUPPORTS_M2M_HOLD_CAPTURE_BUF
to indicate support for this flag.

The device_run() function should look like this:

if (v4l2_m2m_release_capture_buf(out_vb, cap_vb)) {
	v4l2_m2m_buf_done(cap_vb, VB2_BUF_STATE_DONE);
	v4l2_m2m_job_finish(...);
	return;
}
cap_vb->is_held = out_vb->flags & V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF;

...

v4l2_m2m_buf_done(out_vb, VB2_BUF_STATE_DONE);
if (!cap_vb->is_held) {
	v4l2_m2m_buf_done(cap_vb, VB2_BUF_STATE_DONE);
	v4l2_m2m_job_finish(...);
}

In order to handle the corner case where V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF
is always set for the output buffer, and you reached the last frame (so no
new output buffer will be queued with a new timestamp), the driver should
implement support for the V4L2_DEC_CMD_STOP command, and that should do:

struct vb2_v4l2_buffer *out_vb = v4l2_m2m_last_src_buf(m2m_ctx);
struct vb2_v4l2_buffer *cap_vb = v4l2_m2m_last_dst_buf(m2m_ctx);

if (out_vb) {
	out_vb->flags &= ~V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF;
} else if (cap_vb && cap_vb->is_held) {
	v4l2_m2m_buf_done(cap_vb, VB2_BUF_STATE_DONE);
	v4l2_m2m_job_finish(...);
}

At least, I think so. Comments on this are very welcome. We definitely
need better support in v4l2-mem2mem.c for such situations (same for
stateful codecs) since it's too complex for drivers to get right IMHO.

Regards,

	Hans

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
---
 .../media/common/videobuf2/videobuf2-v4l2.c   |  8 +++-
 include/media/v4l2-mem2mem.h                  | 40 +++++++++++++++++++
 include/media/videobuf2-core.h                |  3 ++
 include/media/videobuf2-v4l2.h                |  5 +++
 include/uapi/linux/videodev2.h                | 13 +++---
 5 files changed, 63 insertions(+), 6 deletions(-)

diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
index fb9ac7696fc6..c077d3776840 100644
--- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
+++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
@@ -50,7 +50,8 @@ module_param(debug, int, 0644);
 				 V4L2_BUF_FLAG_TIMESTAMP_MASK)
 /* Output buffer flags that should be passed on to the driver */
 #define V4L2_BUFFER_OUT_FLAGS	(V4L2_BUF_FLAG_PFRAME | V4L2_BUF_FLAG_BFRAME | \
-				 V4L2_BUF_FLAG_KEYFRAME | V4L2_BUF_FLAG_TIMECODE)
+				 V4L2_BUF_FLAG_KEYFRAME | V4L2_BUF_FLAG_TIMECODE | \
+				 V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF)

 /*
  * __verify_planes_array() - verify that the planes array passed in struct
@@ -194,6 +195,7 @@ static int vb2_fill_vb2_v4l2_buffer(struct vb2_buffer *vb, struct v4l2_buffer *b
 	}
 	vbuf->sequence = 0;
 	vbuf->request_fd = -1;
+	vbuf->is_held = false;

 	if (V4L2_TYPE_IS_MULTIPLANAR(b->type)) {
 		switch (b->memory) {
@@ -321,6 +323,8 @@ static int vb2_fill_vb2_v4l2_buffer(struct vb2_buffer *vb, struct v4l2_buffer *b
 		 */
 		vbuf->flags &= ~V4L2_BUF_FLAG_TIMECODE;
 		vbuf->field = b->field;
+		if (!(q->subsystem_flags & VB2_V4L2_FL_SUPPORTS_M2M_HOLD_CAPTURE_BUF))
+			vbuf->flags &= ~V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF;
 	} else {
 		/* Zero any output buffer flags as this is a capture buffer */
 		vbuf->flags &= ~V4L2_BUFFER_OUT_FLAGS;
@@ -659,6 +663,8 @@ static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
 		*caps |= V4L2_BUF_CAP_SUPPORTS_USERPTR;
 	if (q->io_modes & VB2_DMABUF)
 		*caps |= V4L2_BUF_CAP_SUPPORTS_DMABUF;
+	if (q->subsystem_flags & VB2_V4L2_FL_SUPPORTS_M2M_HOLD_CAPTURE_BUF)
+		*caps |= V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF;
 #ifdef CONFIG_MEDIA_CONTROLLER_REQUEST_API
 	if (q->supports_requests)
 		*caps |= V4L2_BUF_CAP_SUPPORTS_REQUESTS;
diff --git a/include/media/v4l2-mem2mem.h b/include/media/v4l2-mem2mem.h
index bb3e63d6bd1a..8263cf108397 100644
--- a/include/media/v4l2-mem2mem.h
+++ b/include/media/v4l2-mem2mem.h
@@ -648,6 +648,46 @@ void v4l2_m2m_buf_copy_metadata(const struct vb2_v4l2_buffer *out_vb,
 				struct vb2_v4l2_buffer *cap_vb,
 				bool copy_frame_flags);

+/**
+ * v4l2_m2m_release_capture_buf() - check if the capture buffer should be
+ * released
+ *
+ * @out_vb: the output buffer
+ * @cap_vb: the capture buffer
+ *
+ * This helper function returns true if the current capture buffer should
+ * be released to vb2. This is the case if the output buffer specified that
+ * the capture buffer should be held (i.e. not returned to vb2) AND if the
+ * timestamp of the capture buffer differs from the output buffer timestamp.
+ *
+ * This helper is to be called at the start of the device_run callback:
+ *
+ * if (v4l2_m2m_release_capture_buf(out_vb, cap_vb)) {
+ *	v4l2_m2m_buf_done(cap_vb, VB2_BUF_STATE_DONE);
+ *	v4l2_m2m_job_finish(...);
+ *	return;
+ * }
+ * cap_vb->is_held = out_vb->flags & V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF;
+ *
+ * ...
+ *
+ * v4l2_m2m_buf_done(out_vb, VB2_BUF_STATE_DONE);
+ * if (!cap_vb->is_held) {
+ *	v4l2_m2m_buf_done(cap_vb, VB2_BUF_STATE_DONE);
+ *	v4l2_m2m_job_finish(...);
+ * }
+ *
+ * This allows for multiple output buffers to be used to fill in a single
+ * capture buffer. This is typically used by stateless decoders where
+ * multiple e.g. H.264 slices contribute to a single decoded frame.
+ */
+static inline bool v4l2_m2m_release_capture_buf(const struct vb2_v4l2_buffer *out_vb,
+						const struct vb2_v4l2_buffer *cap_vb)
+{
+	return cap_vb->is_held && cap_vb->vb2_buf.copied_timestamp &&
+	       out_vb->vb2_buf.timestamp != cap_vb->vb2_buf.timestamp;
+}
+
 /* v4l2 request helper */

 void v4l2_m2m_request_queue(struct media_request *req);
diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index 22f3ff76a8b5..e9d99023c637 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -504,6 +504,8 @@ struct vb2_buf_ops {
  * @buf_ops:	callbacks to deliver buffer information.
  *		between user-space and kernel-space.
  * @drv_priv:	driver private data.
+ * @subsystem_flags: Flags specific to the subsystem (V4L2/DVB/etc.). Not used
+ *		by the vb2 core.
  * @buf_struct_size: size of the driver-specific buffer structure;
  *		"0" indicates the driver doesn't want to use a custom buffer
  *		structure type. for example, ``sizeof(struct vb2_v4l2_buffer)``
@@ -570,6 +572,7 @@ struct vb2_queue {
 	const struct vb2_buf_ops	*buf_ops;

 	void				*drv_priv;
+	u32				subsystem_flags;
 	unsigned int			buf_struct_size;
 	u32				timestamp_flags;
 	gfp_t				gfp_flags;
diff --git a/include/media/videobuf2-v4l2.h b/include/media/videobuf2-v4l2.h
index 8a10889dc2fd..13ab101864aa 100644
--- a/include/media/videobuf2-v4l2.h
+++ b/include/media/videobuf2-v4l2.h
@@ -33,6 +33,7 @@
  * @timecode:	frame timecode.
  * @sequence:	sequence count of this frame.
  * @request_fd:	the request_fd associated with this buffer
+ * @is_held:	if true, then this buffer was held
  * @planes:	plane information (userptr/fd, length, bytesused, data_offset).
  *
  * Should contain enough information to be able to cover all the fields
@@ -46,9 +47,13 @@ struct vb2_v4l2_buffer {
 	struct v4l2_timecode	timecode;
 	__u32			sequence;
 	__s32			request_fd;
+	bool			is_held;
 	struct vb2_plane	planes[VB2_MAX_PLANES];
 };

+/* VB2 V4L2 flags as set in vb2_queue.subsystem_flags */
+#define VB2_V4L2_FL_SUPPORTS_M2M_HOLD_CAPTURE_BUF (1 << 0)
+
 /*
  * to_vb2_v4l2_buffer() - cast struct vb2_buffer * to struct vb2_v4l2_buffer *
  */
diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
index 1050a75fb7ef..26925d63ea05 100644
--- a/include/uapi/linux/videodev2.h
+++ b/include/uapi/linux/videodev2.h
@@ -907,11 +907,12 @@ struct v4l2_requestbuffers {
 };

 /* capabilities for struct v4l2_requestbuffers and v4l2_create_buffers */
-#define V4L2_BUF_CAP_SUPPORTS_MMAP	(1 << 0)
-#define V4L2_BUF_CAP_SUPPORTS_USERPTR	(1 << 1)
-#define V4L2_BUF_CAP_SUPPORTS_DMABUF	(1 << 2)
-#define V4L2_BUF_CAP_SUPPORTS_REQUESTS	(1 << 3)
-#define V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS (1 << 4)
+#define V4L2_BUF_CAP_SUPPORTS_MMAP			(1 << 0)
+#define V4L2_BUF_CAP_SUPPORTS_USERPTR			(1 << 1)
+#define V4L2_BUF_CAP_SUPPORTS_DMABUF			(1 << 2)
+#define V4L2_BUF_CAP_SUPPORTS_REQUESTS			(1 << 3)
+#define V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS		(1 << 4)
+#define V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF	(1 << 5)

 /**
  * struct v4l2_plane - plane info for multi-planar buffers
@@ -1033,6 +1034,8 @@ static inline __u64 v4l2_timeval_to_ns(const struct timeval *tv)
 #define V4L2_BUF_FLAG_IN_REQUEST		0x00000080
 /* timecode field is valid */
 #define V4L2_BUF_FLAG_TIMECODE			0x00000100
+/* Don't return the capture buffer until OUTPUT timestamp changes */
+#define V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF	0x00000200
 /* Buffer is prepared for queuing */
 #define V4L2_BUF_FLAG_PREPARED			0x00000400
 /* Cache handling flags */
-- 
2.20.1


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2019-05-15 12:32 [RFCv2 PATCH] vb2: add V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF Hans Verkuil
2019-05-15 17:01 ` Boris Brezillon

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