Re: [PATCH v12 44/56] media: core: Report the maximum possible number of buffers for the queue
From: Hans Verkuil
Date: Wed Oct 18 2023 - 07:17:31 EST
On 17/10/2023 16:47, 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 | 2 ++
> drivers/media/v4l2-core/v4l2-ioctl.c | 4 ++--
> include/uapi/linux/videodev2.h | 7 ++++++-
> 5 files changed, 17 insertions(+), 5 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..380195c2a00a 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_num_buffers``
> + - If V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS capability flag is set
If -> If the
> + this field indicate the maximum possible number of buffers
indicate -> indicates
> + 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..0b3a41a45d05 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-MAX-NUM-BUFFERS:
>
> .. raw:: latex
>
> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> index f3cf4b235c1f..201438ffd13f 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -680,6 +680,7 @@ 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_MAX_NUM_BUFFERS;
Hmm. This flag is set for both VIDIOC_REQBUFS and _CREATE_BUFS, but the
max_num_buffers field is only reported through VIDIOC_CREATE_BUFS.
I think this flag should be set in vb2_create_bufs() only.
Alternatively, we add a max_num_buffers field to struct v4l2_requestbuffers
as well:
struct v4l2_requestbuffers {
__u32 count;
__u32 type; /* enum v4l2_buf_type */
__u32 memory; /* enum v4l2_memory */
__u32 capabilities;
__u8 flags;
__u8 reserved[1];
__u16 max_num_buffers;
};
Since 32768 is the max for max_num_buffers, this will fit in a u16.
I'm not sure it is worth the effort, though. How likely is it that there
is a driver supporting more than 32 buffers, yet does not support CREATE_BUFS?
So for now, I think it is best to just set this BUF_CAP flag in vb2_create_bufs()
only. But if you have better suggestions, then let me know!
Regards,
Hans
> if (q->io_modes & VB2_MMAP)
> *caps |= V4L2_BUF_CAP_SUPPORTS_MMAP;
> if (q->io_modes & VB2_USERPTR)
> @@ -762,6 +763,7 @@ 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 = vb2_get_num_buffers(q);
> + create->max_num_buffers = q->max_num_buffers;
> if (create->count == 0)
> return ret != -EBUSY ? ret : 0;
>
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 9b1de54ce379..628b013ca0c4 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_num_buffers);
> v4l_print_format(&p->format, write_only);
> }
>
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index c3d4e490ce7c..13ddb5abf584 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -1035,6 +1035,7 @@ 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_MAX_NUM_BUFFERS (1 << 7)
>
> /**
> * struct v4l2_plane - plane info for multi-planar buffers
> @@ -2605,6 +2606,9 @@ 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_num_buffers: if V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS capability flag is set
if -> if the
> + * this field indicate the maximum possible number of buffers
indicate -> indicates
> + * for this queue.
> * @reserved: future extensions
> */
> struct v4l2_create_buffers {
> @@ -2614,7 +2618,8 @@ struct v4l2_create_buffers {
> struct v4l2_format format;
> __u32 capabilities;
> __u32 flags;
> - __u32 reserved[6];
> + __u32 max_num_buffers;
> + __u32 reserved[5];
> };
>
> /*
Regards,
Hans