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

Hans Verkuil
2023-10-02T13:50:29Z

On 02/10/2023 15:46, Benjamin Gaignard wrote:
>
> 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...

Sorry, I meant to reply to the v9 patch, so yes, it is also in v9 :-)

Hans

>
>>
>> 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];
>>>   };
>>>     /*
>>