Re: [REVIEWv3 PATCH 07/13] vb2: reject output buffers with V4L2_FIELD_ALTERNATE

[Archit Taneja <archit@ti.com>]

On Friday 11 April 2014 01:41 PM, Hans Verkuil wrote:
> From: Hans Verkuil <hans.verkuil@cisco.com>
>
> This is not allowed by the spec and does in fact not make any sense.
> Return -EINVAL if this is the case.
>
> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
> Acked-by: Pawel Osciak <pawel@osciak.com>
> Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
>   drivers/media/v4l2-core/videobuf2-core.c | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
>
> diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
> index 6e05495..f8c0247 100644
> --- a/drivers/media/v4l2-core/videobuf2-core.c
> +++ b/drivers/media/v4l2-core/videobuf2-core.c
> @@ -1511,6 +1511,19 @@ static int __buf_prepare(struct vb2_buffer *vb, const struct v4l2_buffer *b)
>   		dprintk(1, "plane parameters verification failed: %d\n", ret);
>   		return ret;
>   	}
> +	if (b->field == V4L2_FIELD_ALTERNATE && V4L2_TYPE_IS_OUTPUT(q->type)) {
> +		/*
> +		 * If the format's field is ALTERNATE, then the buffer's field
> +		 * should be either TOP or BOTTOM, not ALTERNATE since that
> +		 * makes no sense. The driver has to know whether the
> +		 * buffer represents a top or a bottom field in order to
> +		 * program any DMA correctly. Using ALTERNATE is wrong, since
> +		 * that just says that it is either a top or a bottom field,
> +		 * but not which of the two it is.
> +		 */
> +		dprintk(1, "the field is incorrectly set to ALTERNATE for an output buffer\n");
> +		return -EINVAL;
> +	}

If vb2_queue had a field parameter, which tells the format's field type. 
We could have returned an error if the field format was ALTERNATE, and 
the buffer field was not TOP or BOTTOM.

I don't know whether having a field parameter in vb2_queue is a good 
idea or not.

Thanks,
Archit