media: videobuf2: Add min_reqbufs_allocation field to vb2_queue structure

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>

diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
index d8b3c04cb3b5de890fae4db9555719103a35558a..58c495b253ce2965c21e7b8405d7396261fc9731 100644 (file)
--- a/drivers/media/common/videobuf2/videobuf2-core.c
+++ b/drivers/media/common/videobuf2/videobuf2-core.c
@@ -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;

diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
index 667bf9ee1101b8268817161960db6dbab27402d1..4a8b9135cec834032b66dd7c889b1abd558808a2 100644 (file)
--- a/include/media/videobuf2-core.h
+++ b/include/media/videobuf2-core.h
@@ -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];