Re: [PATCH v14 44/56] media: core: Report the maximum possible number of buffers for the queue

Andrzej Pietrasiewicz
2023-11-09T12:29:01Z

Hi Benjamin,

W dniu 31.10.2023 o 17:30, Benjamin Gaignard pisze:
> Use one of the struct v4l2_create_buffers reserved bytes to report

I initially thought you were using literally a single byte, which made
no sense to me given that values much larger than 255 are sometimes going to be
stored there.

Maybe rephrase this to:

Use one element of the struct v4l2_create_buffers "reserved" array to report...

With that you can add my

Reviewed-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>

> the maximum possible number of buffers for the queue.
> V4l2 framework set V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS flags in queue
> capabilities so userland can know when the field is valid.
> Does the same change in v4l2_create_buffers32 structure.
>
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
> ---
> .../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-compat-ioctl32.c | 9 ++++++++-
> drivers/media/v4l2-core/v4l2-ioctl.c | 4 ++--
> include/uapi/linux/videodev2.h | 7 ++++++-
> 6 files changed, 25 insertions(+), 6 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..49232c9006c2 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 the V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS capability flag is set
> + this field indicates 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..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..bdfc3a253c65 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -762,6 +762,8 @@ 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;
> + create->capabilities |= V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS;
> if (create->count == 0)
> return ret != -EBUSY ? ret : 0;
>
> diff --git a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> index f3bed37859a2..5aac5cf780b3 100644
> --- a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> +++ b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
> @@ -116,6 +116,9 @@ struct v4l2_format32 {
> * @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
> + * this field indicate the maximum possible number of buffers
> + * for this queue.
> * @reserved: future extensions
> */
> struct v4l2_create_buffers32 {
> @@ -125,7 +128,8 @@ struct v4l2_create_buffers32 {
> struct v4l2_format32 format;
> __u32 capabilities;
> __u32 flags;
> - __u32 reserved[6];
> + __u32 max_num_buffers;
> + __u32 reserved[5];
> };
>
> static int get_v4l2_format32(struct v4l2_format *p64,
> @@ -175,6 +179,8 @@ static int get_v4l2_create32(struct v4l2_create_buffers *p64,
> return -EFAULT;
> if (copy_from_user(&p64->flags, &p32->flags, sizeof(p32->flags)))
> return -EFAULT;
> + if (copy_from_user(&p64->max_num_buffers, &p32->max_num_buffers, sizeof(p32->max_num_buffers)))
> + return -EFAULT;
> return get_v4l2_format32(&p64->format, &p32->format);
> }
>
> @@ -221,6 +227,7 @@ static int put_v4l2_create32(struct v4l2_create_buffers *p64,
> offsetof(struct v4l2_create_buffers32, format)) ||
> put_user(p64->capabilities, &p32->capabilities) ||
> put_user(p64->flags, &p32->flags) ||
> + put_user(p64->max_num_buffers, &p32->max_num_buffers) ||
> copy_to_user(p32->reserved, p64->reserved, sizeof(p64->reserved)))
> return -EFAULT;
> return put_v4l2_format32(&p64->format, &p32->format);
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 9b1de54ce379..4d90424cbfc4 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 num 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
> + * this field indicate the maximum possible number of buffers
> + * 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];
> };
>
> /*