Re: [PATCH] media: vb2: refactor setting flags and caps, fix missing cap

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Hi Hans,

On Tue, Jan 16, 2024 at 11:05 PM Hans Verkuil <hverkuil-cisco@xxxxxxxxx> wrote:
>
> Several functions implementing VIDIOC_REQBUFS and _CREATE_BUFS all use almost
> the same code to fill in the flags and capability fields. Refactor this into a
> new vb2_set_flags_and_caps() function that replaces the old fill_buf_caps()
> and validate_memory_flags() functions.
>
> This also fixes a bug where vb2_ioctl_create_bufs() would not set the
> V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS cap and also not fill in the
> max_num_buffers field.
>
> Fixes: d055a76c0065 ("media: core: Report the maximum possible number of buffers for the queue")
> Signed-off-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
> ---
>  .../media/common/videobuf2/videobuf2-v4l2.c   | 55 +++++++++----------
>  1 file changed, 26 insertions(+), 29 deletions(-)
>

Thanks for the patch! Please check my comments inline.

> diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> index 54d572c3b515..c575198e8354 100644
> --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> @@ -671,8 +671,20 @@ int vb2_querybuf(struct vb2_queue *q, struct v4l2_buffer *b)
>  }
>  EXPORT_SYMBOL(vb2_querybuf);
>
> -static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
> +static void vb2_set_flags_and_caps(struct vb2_queue *q, u32 memory,
> +                                  u32 *flags, u32 *caps, u32 *max_num_bufs)
>  {
> +       if (!q->allow_cache_hints || memory != V4L2_MEMORY_MMAP) {
> +               /*
> +                * This needs to clear V4L2_MEMORY_FLAG_NON_COHERENT only,
> +                * but in order to avoid bugs we zero out all bits.
> +                */
> +               *flags = 0;
> +       } else {
> +               /* Clear all unknown flags. */
> +               *flags &= V4L2_MEMORY_FLAG_NON_COHERENT;
> +       }
> +
>         *caps = V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS;
>         if (q->io_modes & VB2_MMAP)
>                 *caps |= V4L2_BUF_CAP_SUPPORTS_MMAP;
> @@ -686,21 +698,9 @@ static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
>                 *caps |= V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS;
>         if (q->supports_requests)
>                 *caps |= V4L2_BUF_CAP_SUPPORTS_REQUESTS;
> -}
> -
> -static void validate_memory_flags(struct vb2_queue *q,
> -                                 int memory,
> -                                 u32 *flags)
> -{
> -       if (!q->allow_cache_hints || memory != V4L2_MEMORY_MMAP) {
> -               /*
> -                * This needs to clear V4L2_MEMORY_FLAG_NON_COHERENT only,
> -                * but in order to avoid bugs we zero out all bits.
> -                */
> -               *flags = 0;
> -       } else {
> -               /* Clear all unknown flags. */
> -               *flags &= V4L2_MEMORY_FLAG_NON_COHERENT;
> +       if (max_num_bufs) {
> +               *max_num_bufs = q->max_num_buffers;
> +               *caps |= V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS;
>         }
>  }
>
> @@ -709,8 +709,8 @@ int vb2_reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
>         int ret = vb2_verify_memory_type(q, req->memory, req->type);
>         u32 flags = req->flags;

I think we have a bug here, we check the memory type, but just let the
code continue even if it's invalid.

>
> -       fill_buf_caps(q, &req->capabilities);
> -       validate_memory_flags(q, req->memory, &flags);
> +       vb2_set_flags_and_caps(q, req->memory, &flags,
> +                              &req->capabilities, NULL);
>         req->flags = flags;
>         return ret ? ret : vb2_core_reqbufs(q, req->memory,
>                                             req->flags, &req->count);
> @@ -751,11 +751,9 @@ int vb2_create_bufs(struct vb2_queue *q, struct v4l2_create_buffers *create)
>         int ret = vb2_verify_memory_type(q, create->memory, f->type);
>         unsigned i;
>

Ditto.

> -       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;
> +       vb2_set_flags_and_caps(q, create->memory, &create->flags,
> +                              &create->capabilities, &create->max_num_buffers);
>         if (create->count == 0)
>                 return ret != -EBUSY ? ret : 0;
>
> @@ -1006,8 +1004,8 @@ int vb2_ioctl_reqbufs(struct file *file, void *priv,
>         int res = vb2_verify_memory_type(vdev->queue, p->memory, p->type);
>         u32 flags = p->flags;
>
> -       fill_buf_caps(vdev->queue, &p->capabilities);
> -       validate_memory_flags(vdev->queue, p->memory, &flags);
> +       vb2_set_flags_and_caps(vdev->queue, p->memory, &flags,
> +                              &p->capabilities, NULL);

Could we just call vb2_reqbufs() instead of vb2_core_reqbufs() and
avoid all the duplicate checks?

>         p->flags = flags;
>         if (res)
>                 return res;
> @@ -1026,12 +1024,11 @@ int vb2_ioctl_create_bufs(struct file *file, void *priv,
>                           struct v4l2_create_buffers *p)
>  {
>         struct video_device *vdev = video_devdata(file);
> -       int res = vb2_verify_memory_type(vdev->queue, p->memory,
> -                       p->format.type);
> +       int res = vb2_verify_memory_type(vdev->queue, p->memory, p->format.type);
>
> -       p->index = vdev->queue->num_buffers;
> -       fill_buf_caps(vdev->queue, &p->capabilities);
> -       validate_memory_flags(vdev->queue, p->memory, &p->flags);
> +       p->index = vb2_get_num_buffers(vdev->queue);
> +       vb2_set_flags_and_caps(vdev->queue, p->memory, &p->flags,
> +                              &p->capabilities, &p->max_num_buffers);

This function in fact already calls vb2_create_bufs() which includes
all the checks above, except the one for vb2_queue_is_bus() that
continues down below, so maybe we can just remove them?

Best regards,
Tomasz

>         /*
>          * If count == 0, then just check if memory and type are valid.
>          * Any -EBUSY result from vb2_verify_memory_type can be mapped to 0.
> --
> 2.42.0
>
>





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