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

[Andrzej Pietrasiewicz <andrzej.p@collabora.com>]

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];
>   };
>   
>   /*


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