[media] media: vb2: change queue initialization order

This patch changes the order of operations during stream on call. Now the
buffers are first queued to the driver and then the start_streaming method
is called.

This resolves the most common case when the driver needs to know buffer
addresses to enable dma engine and start streaming. Additional parameter
to start_streaming method have been added to simplify drivers code. The
driver are now obliged to check if the number of queued buffers is high
enough to enable hardware streaming. If not - it can return an error. In
such case all the buffers that have been pre-queued are invalidated.

This patch also updates all videobuf2 clients to work properly with the
changed order of operations.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
CC: Pawel Osciak <pawel@osciak.com>
CC: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
CC: Hans Verkuil <hverkuil@xs4all.nl>
CC: Tomasz Stanislawski <t.stanislaws@samsung.com>
CC: Sylwester Nawrocki <s.nawrocki@samsung.com>
CC: Kamil Debski <k.debski@samsung.com>
CC: Jonathan Corbet <corbet@lwn.net>
CC: Josh Wu <josh.wu@atmel.com>
CC: Hans de Goede <hdegoede@redhat.com>
CC: Paul Mundt <lethal@linux-sh.org>
Tested-by: Josh Wu <josh.wu@atmel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 13 insertions, 4 deletions

diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index 5287e901e17..ea55c08eddf 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -196,15 +196,24 @@ struct vb2_buffer {
  *			before userspace accesses the buffer; optional
  * @buf_cleanup:	called once before the buffer is freed; drivers may
  *			perform any additional cleanup; optional
- * @start_streaming:	called once before entering 'streaming' state; enables
- *			driver to receive buffers over buf_queue() callback
+ * @start_streaming:	called once to enter 'streaming' state; the driver may
+ *			receive buffers with @buf_queue callback before
+ *			@start_streaming is called; the driver gets the number
+ *			of already queued buffers in count parameter; driver
+ *			can return an error if hardware fails or not enough
+ *			buffers has been queued, in such case all buffers that
+ *			have been already given by the @buf_queue callback are
+ *			invalidated.
  * @stop_streaming:	called when 'streaming' state must be disabled; driver
  *			should stop any DMA transactions or wait until they
  *			finish and give back all buffers it got from buf_queue()
  *			callback; may use vb2_wait_for_all_buffers() function
  * @buf_queue:		passes buffer vb to the driver; driver may start
  *			hardware operation on this buffer; driver should give
- *			the buffer back by calling vb2_buffer_done() function
+ *			the buffer back by calling vb2_buffer_done() function;
+ *			it is allways called after calling STREAMON ioctl;
+ *			might be called before start_streaming callback if user
+ *			pre-queued buffers before calling STREAMON
  */
 struct vb2_ops {
 	int (*queue_setup)(struct vb2_queue *q, unsigned int *num_buffers,
@@ -219,7 +228,7 @@ struct vb2_ops {
 	int (*buf_finish)(struct vb2_buffer *vb);
 	void (*buf_cleanup)(struct vb2_buffer *vb);
 
-	int (*start_streaming)(struct vb2_queue *q);
+	int (*start_streaming)(struct vb2_queue *q, unsigned int count);
 	int (*stop_streaming)(struct vb2_queue *q);
 
 	void (*buf_queue)(struct vb2_buffer *vb);