Re: [PATCH] media: m2m-deinterlace: fix default capture field

[Jacopo Mondi <jacopo.mondi@ideasonboard.com>]

Hi Xu Rao

On Tue, Aug 11, 2026 at 09:52:22AM +0800, raoxu wrote:
> From: Xu Rao <raoxu@uniontech.com>
>
> queue_init() initializes default formats for both the source and capture
> queues.  It first sets the source field to V4L2_FIELD_SEQ_TB, but then
> stores the capture default, V4L2_FIELD_INTERLACED_TB, in the source queue
> again while initializing the capture queue.
>
> This overwrites the valid source default and leaves the capture field at
> its zero-initialized value, V4L2_FIELD_ANY.  vidioc_streamon() accepts
> only V4L2_FIELD_SEQ_TB or V4L2_FIELD_SEQ_BT on the source queue, and
> requires the capture queue to use a compatible interlaced or NONE field.
> Userspace that relies on the default formats can therefore get -EINVAL
> when starting streaming.
>
> Initialize the capture field instead.  The bug is usually hidden because
> mem2mem applications commonly call S_FMT on both queues before streaming;
> the TRY_FMT paths normalize the fields and S_FMT overwrites q_data[].field.
>
> Fixes: 8f0755c06b90 ("[media] media: Add mem2mem deinterlacing driver")

Missing

Cc: stable@vger.kernel.org

> Signed-off-by: Xu Rao <raoxu@uniontech.com>
> ---
>  drivers/media/platform/m2m-deinterlace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/media/platform/m2m-deinterlace.c b/drivers/media/platform/m2m-deinterlace.c
> index 1d0e70eaea3d..9dcc4bd6cbdd 100644
> --- a/drivers/media/platform/m2m-deinterlace.c
> +++ b/drivers/media/platform/m2m-deinterlace.c
> @@ -822,7 +822,7 @@ static int queue_init(void *priv, struct vb2_queue *src_vq,
>  	q_data[V4L2_M2M_DST].width = 640;
>  	q_data[V4L2_M2M_DST].height = 480;
>  	q_data[V4L2_M2M_DST].sizeimage = (640 * 480 * 3) / 2;
> -	q_data[V4L2_M2M_SRC].field = V4L2_FIELD_INTERLACED_TB;
> +	q_data[V4L2_M2M_DST].field = V4L2_FIELD_INTERLACED_TB;

Looks like a bug indeed. As you said, set_fmt re-initializes the field
to V4L2_FIELD_INTERLACED_TB so it should be harmless, but there are no
reasons not to fix the initialization.

Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>

>
>  	return vb2_queue_init(dst_vq);
>  }
> --
> 2.50.1
>