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media: videobuf2: Add min_reqbufs_allocation field to vb2_queue structure

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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@collabora.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
This commit is contained in:
Benjamin Gaignard 2024-03-14 16:32:19 +01:00 committed by Hans Verkuil
parent d7cdb5946f
commit 6662edcd32
2 changed files with 37 additions and 16 deletions
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38
drivers/media/common/videobuf2/videobuf2-core.c
View file

@ -866,7 +866,7 @@ 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));
/*
@ -918,7 +918,7 @@ 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;
/*
@ -2524,6 +2524,25 @@ 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;

15
include/media/videobuf2-core.h
View file

@ -549,9 +549,21 @@ 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.
* @alloc_devs: &struct device memory type/allocator-specific per-plane device
*/
/*
@ -622,6 +634,7 @@ 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];