Re: [PATCH v15 11/19] media: uvcvideo: add support for compound controls

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 14-Nov-24 8:10 PM, Ricardo Ribalda wrote:
> From: Yunke Cao <yunkec@google.com>
> 
> This patch adds support for compound controls. This is required to
> support controls that cannot be represented with a s64 data, such as the
> Region of Interest.
> 
> Signed-off-by: Yunke Cao <yunkec@google.com>
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> ---
>  drivers/media/usb/uvc/uvc_ctrl.c | 224 ++++++++++++++++++++++++++++++++-------
>  drivers/media/usb/uvc/uvcvideo.h |   5 +
>  2 files changed, 192 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> index 893d12cd3f90..e51cd0a2228a 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c

<snip>

> @@ -1971,19 +2009,59 @@ int __uvc_ctrl_commit(struct uvc_fh *handle, int rollback,
>  	return ret;
>  }
>  
> -int uvc_ctrl_get(struct uvc_video_chain *chain, u32 which,
> -		 struct v4l2_ext_control *xctrl)
> +static int uvc_mapping_get_xctrl_compound(struct uvc_video_chain *chain,
> +					  struct uvc_control *ctrl,
> +					  struct uvc_control_mapping *mapping,
> +					  u32 which,
> +					  struct v4l2_ext_control *xctrl)
>  {
> -	struct uvc_control *ctrl;
> -	struct uvc_control_mapping *mapping;
> -
> -	if (__uvc_query_v4l2_class(chain, xctrl->id, 0) >= 0)
> -		return -EACCES;
> +	u8 *data __free(kfree) = NULL;
> +	size_t size;
> +	u8 query;
> +	int ret;
> +	int id;
>  
> -	ctrl = uvc_find_control(chain, xctrl->id, &mapping);
> -	if (ctrl == NULL)
> +	switch (which) {
> +	case V4L2_CTRL_WHICH_CUR_VAL:
> +		ret = __uvc_ctrl_load_cur(chain, ctrl);
> +		if (ret < 0)
> +			return ret;
> +		id = UVC_CTRL_DATA_CURRENT;
> +		query = UVC_GET_CUR;
> +		break;
> +	case V4L2_CTRL_WHICH_DEF_VAL:
> +		ret = uvc_ctrl_populate_cache(chain, ctrl);
> +		if (ret < 0)
> +			return ret;
> +		id = UVC_CTRL_DATA_DEF;
> +		query = UVC_GET_DEF;
> +		break;
> +	default:
>  		return -EINVAL;
> +	}
> +
> +	size = DIV_ROUND_UP(mapping->size, 8);
> +	if (xctrl->size < size) {
> +		xctrl->size = size;
> +		return -ENOSPC;
> +	}
> +
> +	data = kmalloc(size, GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	ret = mapping->get(mapping, query, uvc_ctrl_data(ctrl, id), size, data);
> +	if (ret < 0)
> +		return ret;
> +
> +	return copy_to_user(xctrl->ptr, data, size) ? -EFAULT : 0;
> +}

While reviewing "[PATCH v15 14/19] media: uvcvideo: Use the camera to clamp compound controls"
I realized that this copy_to_user() is somewhat unexpected. Normally we let the v4l2 core
ioctl wrapper take care of this.

Since there is no room in struct v4l2_ext_control to store the data I guess this is ok,
but IMHO this does at least need a comment explaining how this is a special case.

Regards,

Hans