Re: [PATCH v8 13/53] media: Report the maximum possible number of buffers for the queue

[Hans Verkuil]

On 27/09/2023 17:35, Benjamin Gaignard wrote:
> Use one of the struct v4l2_create_buffers reserved bytes to report
> the maximum possible number of buffers for the queue.
> V4l2 framework set V4L2_BUF_CAP_SUPPORTS_SET_MAX_BUFS flags in queue
> capabilities so userland can know when the field is valid.
> 
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@xxxxxxxxxxxxx>
> ---
>  .../userspace-api/media/v4l/vidioc-create-bufs.rst       | 8 ++++++--
>  Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst | 1 +
>  drivers/media/common/videobuf2/videobuf2-v4l2.c          | 9 +++++++--
>  drivers/media/v4l2-core/v4l2-ioctl.c                     | 4 ++--
>  include/uapi/linux/videodev2.h                           | 7 ++++++-
>  5 files changed, 22 insertions(+), 7 deletions(-)
> 
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> index a048a9f6b7b6..1a46549e7462 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-create-bufs.rst
> @@ -116,9 +116,13 @@ than the number requested.
>        - ``flags``
>        - Specifies additional buffer management attributes.
>  	See :ref:`memory-flags`.
> -
>      * - __u32
> -      - ``reserved``\ [6]
> +      - ``max_buffers``
> +      - If V4L2_BUF_CAP_SUPPORTS_SET_MAX_BUFS capability flag is set
> +        this field indicate the maximum possible number of buffers
> +        for this queue.
> +    * - __u32
> +      - ``reserved``\ [5]
>        - A place holder for future extensions. Drivers and applications
>  	must set the array to zero.
>  
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> index 099fa6695167..0395187e1a5a 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst
> @@ -120,6 +120,7 @@ aborting or finishing any DMA in progress, an implicit
>  .. _V4L2-BUF-CAP-SUPPORTS-ORPHANED-BUFS:
>  .. _V4L2-BUF-CAP-SUPPORTS-M2M-HOLD-CAPTURE-BUF:
>  .. _V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS:
> +.. _V4L2-BUF-CAP-SUPPORTS-SET-MAX-BUFS:
>  
>  .. raw:: latex
>  
> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> index 278ea1107b01..655133f1ae2b 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -686,6 +686,7 @@ EXPORT_SYMBOL(vb2_querybuf);
>  static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
>  {
>  	*caps = V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS;
> +	*caps |= V4L2_BUF_CAP_SUPPORTS_SET_MAX_BUFS;
>  	if (q->io_modes & VB2_MMAP)
>  		*caps |= V4L2_BUF_CAP_SUPPORTS_MMAP;
>  	if (q->io_modes & VB2_USERPTR)
> @@ -767,9 +768,13 @@ int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
>  
>  	fill_buf_caps(q, &create->capabilities);
>  	validate_memory_flags(q, create->memory, &create->flags);
> -	create->index = q->num_buffers;
> -	if (create->count == 0)
> +
> +	create->max_buffers = q->max_num_buffers;
> +
> +	if (create->count == 0) {
> +		create->index = vb2_get_num_buffers(q);

This breaks git bisect: this function isn't introduced until patch 21/53.

Note: with the build scripts you can just run it with:

./build.sh -patches 53 ...

and it will apply each patch in sequence and attempt to compile it.

Regards,

	Hans

>  		return ret != -EBUSY ? ret : 0;
> +	}
>  
>  	switch (f->type) {
>  	case V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE:
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index f4d9d6279094..700db197e371 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -483,9 +483,9 @@ static void v4l_print_create_buffers(const void *arg, bool write_only)
>  {
>  	const struct v4l2_create_buffers *p = arg;
>  
> -	pr_cont("index=%d, count=%d, memory=%s, capabilities=0x%08x, ",
> +	pr_cont("index=%d, count=%d, memory=%s, capabilities=0x%08x, max buffers=%u",
>  		p->index, p->count, prt_names(p->memory, v4l2_memory_names),
> -		p->capabilities);
> +		p->capabilities, p->max_buffers);
>  	v4l_print_format(&p->format, write_only);
>  }
>  
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 78260e5d9985..b0dbb1be728c 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -1034,6 +1034,7 @@ struct v4l2_requestbuffers {
>  #define V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS		(1 << 4)
>  #define V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF	(1 << 5)
>  #define V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS		(1 << 6)
> +#define V4L2_BUF_CAP_SUPPORTS_SET_MAX_BUFS		(1 << 7)
>  
>  /**
>   * struct v4l2_plane - plane info for multi-planar buffers
> @@ -2604,6 +2605,9 @@ struct v4l2_dbg_chip_info {
>   * @flags:	additional buffer management attributes (ignored unless the
>   *		queue has V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS capability
>   *		and configured for MMAP streaming I/O).
> + * @max_buffers: if V4L2_BUF_CAP_SUPPORTS_SET_MAX_BUFS capability flag is set
> + *		 this field indicate the maximum possible number of buffers
> + *		 for this queue.
>   * @reserved:	future extensions
>   */
>  struct v4l2_create_buffers {
> @@ -2613,7 +2617,8 @@ struct v4l2_create_buffers {
>  	struct v4l2_format	format;
>  	__u32			capabilities;
>  	__u32			flags;
> -	__u32			reserved[6];
> +	__u32			max_buffers;
> +	__u32			reserved[5];
>  };
>  
>  /*