Add 'min_reqbufs_allocation' field in the vb2_queue structure so drivers
can specify the minimum number of buffers to allocate when calling
VIDIOC_REQBUFS.
When initializing the queue, v4l2 core makes sure that the following
constraints are respected:
- the minimum number of buffers to allocate must be at least 2 because
one buffer is used by the hardware while the other is being processed
by userspace.
-if the driver needs 'min_queued_buffers' in the queue before calling
start_streaming(), then the minimum requirement is 'min_queued_buffers + 1'
to keep at least one buffer available for userspace.
Simplify __vb2_init_fileio() by using 'min_reqbufs_allocation' directly
to avoid duplicating the minimum number of buffers to allocate computation.
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@xxxxxxxxxxxxx>
---
.../media/common/videobuf2/videobuf2-core.c | 38 +++++++++++--------
include/media/videobuf2-core.h | 15 +++++++-
2 files changed, 37 insertions(+), 16 deletions(-)
diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
index 8aa6057df581..85a56b7fcd4a 100644
--- a/drivers/media/common/videobuf2/videobuf2-core.c
+++ b/drivers/media/common/videobuf2/videobuf2-core.c
@@ -867,7 +867,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
/*
* Make sure the requested values and current defaults are sane.
*/
- num_buffers = max_t(unsigned int, *count, q->min_queued_buffers);
+ num_buffers = max_t(unsigned int, *count, q->min_reqbufs_allocation);
num_buffers = min_t(unsigned int, num_buffers, q->max_num_buffers);
memset(q->alloc_devs, 0, sizeof(q->alloc_devs));
/*
@@ -919,7 +919,7 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
* There is no point in continuing if we can't allocate the minimum
* number of buffers needed by this vb2_queue.
*/
- if (allocated_buffers < q->min_queued_buffers)
+ if (allocated_buffers < q->min_reqbufs_allocation)
ret = -ENOMEM;
/*
@@ -2525,6 +2525,25 @@ int vb2_core_queue_init(struct vb2_queue *q)
if (WARN_ON(q->supports_requests && q->min_queued_buffers))
return -EINVAL;
+ /*
+ * The minimum requirement is 2: one buffer is used
+ * by the hardware while the other is being processed by userspace.
+ */
+ if (q->min_reqbufs_allocation < 2)
+ q->min_reqbufs_allocation = 2;
+
+ /*
+ * If the driver needs 'min_queued_buffers' in the queue before
+ * calling start_streaming() then the minimum requirement is
+ * 'min_queued_buffers + 1' to keep at least one buffer available
+ * for userspace.
+ */
+ if (q->min_reqbufs_allocation < q->min_queued_buffers + 1)
+ q->min_reqbufs_allocation = q->min_queued_buffers + 1;
+
+ if (WARN_ON(q->min_reqbufs_allocation > q->max_num_buffers))
+ return -EINVAL;
+
INIT_LIST_HEAD(&q->queued_list);
INIT_LIST_HEAD(&q->done_list);
spin_lock_init(&q->done_lock);
@@ -2717,7 +2736,6 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
struct vb2_fileio_data *fileio;
struct vb2_buffer *vb;
int i, ret;
- unsigned int count = 0;
/*
* Sanity check
@@ -2738,18 +2756,8 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
if (q->streaming || vb2_get_num_buffers(q) > 0)
return -EBUSY;
- /*
- * Start with q->min_queued_buffers + 1, driver can increase it in
- * queue_setup()
- *
- * 'min_queued_buffers' buffers need to be queued up before you
- * can start streaming, plus 1 for userspace (or in this case,
- * kernelspace) processing.
- */
- count = max(2, q->min_queued_buffers + 1);
-
dprintk(q, 3, "setting up file io: mode %s, count %d, read_once %d, write_immediately %d\n",
- (read) ? "read" : "write", count, q->fileio_read_once,
+ (read) ? "read" : "write", q->min_reqbufs_allocation, q->fileio_read_once,
q->fileio_write_immediately);
fileio = kzalloc(sizeof(*fileio), GFP_KERNEL);
@@ -2763,7 +2771,7 @@ static int __vb2_init_fileio(struct vb2_queue *q, int read)
* Request buffers and use MMAP type to force driver
* to allocate buffers by itself.
*/
- fileio->count = count;
+ fileio->count = q->min_reqbufs_allocation;
fileio->memory = VB2_MEMORY_MMAP;
fileio->type = q->type;
q->fileio = fileio;
diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index b317286a7b08..ef5500d14c09 100644
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -550,9 +550,21 @@ struct vb2_buf_ops {
* @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.
- * VIDIOC_REQBUFS will ensure at least @min_queued_buffers
+ * VIDIOC_REQBUFS will ensure at least @min_queued_buffers + 1
* buffers will be allocated. Note that VIDIOC_CREATE_BUFS will not
* modify the requested buffer count.
+ * @min_reqbufs_allocation: the minimum number of buffers to be allocated when
+ * calling VIDIOC_REQBUFS. Note that VIDIOC_CREATE_BUFS will *not*
+ * modify the requested buffer count and does not use this field.
+ * Drivers can set this if there has to be a certain number of
+ * buffers available for the hardware to work effectively.
+ * This allows calling VIDIOC_REQBUFS with a buffer count of 1 and
+ * it will be automatically adjusted to a workable buffer count.
+ * If set, then @min_reqbufs_allocation must be larger than
+ * @min_queued_buffers + 1.
+ * If this field is > 3, then it is highly recommended that the
+ * driver implements the V4L2_CID_MIN_BUFFERS_FOR_CAPTURE/OUTPUT
+ * control.
*/
/*
* Private elements (won't appear at the uAPI book):
@@ -619,6 +631,7 @@ struct vb2_queue {
u32 timestamp_flags;
gfp_t gfp_flags;
u32 min_queued_buffers;
+ u32 min_reqbufs_allocation;
struct device *alloc_devs[VB2_MAX_PLANES];
--
2.40.1
