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authorHans Verkuil <hans.verkuil@cisco.com>2014-02-24 13:51:03 -0300
committerMauro Carvalho Chehab <m.chehab@samsung.com>2014-03-11 06:56:41 -0300
commitb3379c6201bb3555298cdbf0aa004af260f2a6a4 (patch)
tree936271737c6bdcf27a40d0af2ad9ab0d2f5533fa /include/media/videobuf2-core.h
parenta7afcaccfab2fb012841852eaead79861dc9cb5f (diff)
[media] vb2: only call start_streaming if sufficient buffers are queued
In commit 02f142ecd24aaf891324ffba8527284c1731b561 support was added to start_streaming to return -ENOBUFS if insufficient buffers were queued for the DMA engine to start. The vb2 core would attempt calling start_streaming again if another buffer would be queued up. Later analysis uncovered problems with the queue management if start_streaming would return an error: the buffers are enqueued to the driver before the start_streaming op is called, so after an error they are never returned to the vb2 core. The solution for this is to let the driver return them to the vb2 core in case of an error while starting the DMA engine. However, in the case of -ENOBUFS that would be weird: it is not a real error, it just says that more buffers are needed. Requiring start_streaming to give them back only to have them requeued again the next time the application calls QBUF is inefficient. This patch changes this mechanism: it adds a 'min_buffers_needed' field to vb2_queue that drivers can set with the minimum number of buffers required to start the DMA engine. The start_streaming op is only called if enough buffers are queued. The -ENOBUFS handling has been dropped in favor of this new method. Drivers are expected to return buffers back to vb2 core with state QUEUED if start_streaming would return an error. The vb2 core checks for this and produces a warning if that didn't happen and it will forcefully reclaim such buffers to ensure that the internal vb2 core state remains consistent and all buffer-related resources have been correctly freed and all op calls have been balanced. __reqbufs() has been updated to check that at least min_buffers_needed buffers could be allocated. If fewer buffers were allocated then __reqbufs will free what was allocated and return -ENOMEM. Based on a suggestion from Pawel Osciak. __create_bufs() doesn't do that check, since the use of __create_bufs assumes some advance scenario where the user might want more control. Instead streamon will check if enough buffers were allocated to prevent streaming with fewer than the minimum required number of buffers. Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
Diffstat (limited to 'include/media/videobuf2-core.h')
-rw-r--r--include/media/videobuf2-core.h14
1 files changed, 10 insertions, 4 deletions
diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index 36e3e8e2d457..af4621109726 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -356,20 +356,24 @@ struct v4l2_fh;
* @gfp_flags: additional gfp flags used when allocating the buffers.
* Typically this is 0, but it may be e.g. GFP_DMA or __GFP_DMA32
* to force the buffer allocation to a specific memory zone.
+ * @min_buffers_needed: the minimum number of buffers needed before
+ * start_streaming() can be called. Used when a DMA engine
+ * cannot be started unless at least this number of buffers
+ * have been queued into the driver.
*
* @memory: current memory type used
* @bufs: videobuf buffer structures
* @num_buffers: number of allocated/used buffers
* @queued_list: list of buffers currently queued from userspace
+ * @queued_count: number of buffers queued and ready for streaming.
* @owned_by_drv_count: number of buffers owned by the driver
* @done_list: list of buffers ready to be dequeued to userspace
* @done_lock: lock to protect done_list list
* @done_wq: waitqueue for processes waiting for buffers ready to be dequeued
* @alloc_ctx: memory type/allocator-specific contexts for each plane
* @streaming: current streaming state
- * @retry_start_streaming: start_streaming() was called, but there were not enough
- * buffers queued. If set, then retry calling start_streaming when
- * queuing a new buffer.
+ * @start_streaming_called: start_streaming() was called successfully and we
+ * started streaming.
* @fileio: file io emulator internal data, used only if emulator is active
*/
struct vb2_queue {
@@ -385,6 +389,7 @@ struct vb2_queue {
unsigned int buf_struct_size;
u32 timestamp_flags;
gfp_t gfp_flags;
+ u32 min_buffers_needed;
/* private: internal use only */
enum v4l2_memory memory;
@@ -392,6 +397,7 @@ struct vb2_queue {
unsigned int num_buffers;
struct list_head queued_list;
+ unsigned int queued_count;
atomic_t owned_by_drv_count;
struct list_head done_list;
@@ -402,7 +408,7 @@ struct vb2_queue {
unsigned int plane_sizes[VIDEO_MAX_PLANES];
unsigned int streaming:1;
- unsigned int retry_start_streaming:1;
+ unsigned int start_streaming_called:1;
struct vb2_fileio_data *fileio;

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