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

[Benjamin Gaignard <benjamin.gaignard@collabora.com>]

Le 02/10/2023 à 15:37, Hans Verkuil a écrit :
> 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@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          | 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.

It should  be create->index = q->num_buffers;
The error is also in v9...

>
> 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];
>>   };
>>   
>>   /*
>