usb: gadget: f_uvc: Expose configuration name through video node

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Kieran,

Thank you for the patch.

On Wednesday, 23 May 2018 23:39:47 EEST Kieran Bingham wrote:
> From: Kieran Bingham <kieran.bingham@ideasonboard.com>
> 
> When utilising multiple instantiations of a UVC gadget on a composite
> device, there is no clear method to link a particular configuration to
> its respective video node.
> 
> Provide a means for identifying the correct video node by exposing the
> name of the function configuration through sysfs.
> 
> Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
> ---
>  drivers/usb/gadget/function/f_uvc.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/gadget/function/f_uvc.c
> b/drivers/usb/gadget/function/f_uvc.c index 1affa8e3a974..f326d1707633
> 100644
> --- a/drivers/usb/gadget/function/f_uvc.c
> +++ b/drivers/usb/gadget/function/f_uvc.c
> @@ -421,10 +421,21 @@ uvc_function_disconnect(struct uvc_device *uvc)
>   * USB probe and disconnect
>   */
> 
> +static ssize_t config_show(struct device *dev, struct device_attribute
> *attr, +			   char *buf)
> +{
> +	struct uvc_device *uvc = dev_get_drvdata(dev);
> +
> +	return sprintf(buf, "%s\n", uvc->func.fi->group.cg_item.ci_name);
> +}
> +
> +static DEVICE_ATTR_RO(config);

You need to document the attribute in Documentation/ABI/.

I wonder whether we should use a more explicit name for the attribute. Maybe 
function_name ? usb_function_name ? usb_configfs_name ? Feel free to propose a 
better option.

> +
>  static int
>  uvc_register_video(struct uvc_device *uvc)
>  {
>  	struct usb_composite_dev *cdev = uvc->func.config->cdev;
> +	int ret;
> 
>  	/* TODO reference counting. */
>  	uvc->vdev.v4l2_dev = &uvc->v4l2_dev;
> @@ -437,7 +448,17 @@ uvc_register_video(struct uvc_device *uvc)
> 
>  	video_set_drvdata(&uvc->vdev, uvc);
> 
> -	return video_register_device(&uvc->vdev, VFL_TYPE_GRABBER, -1);
> +	ret = video_register_device(&uvc->vdev, VFL_TYPE_GRABBER, -1);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = device_create_file(&uvc->vdev.dev, &dev_attr_config);
> +	if (ret < 0) {
> +		video_unregister_device(&uvc->vdev);
> +		return ret;
> +	}
> +
> +	return 0;
>  }
> 
>  #define UVC_COPY_DESCRIPTOR(mem, dst, desc) \
> @@ -875,6 +896,7 @@ static void uvc_unbind(struct usb_configuration *c,
> struct usb_function *f)
> 
>  	INFO(cdev, "%s\n", __func__);
> 
> +	device_remove_file(&uvc->vdev.dev, &dev_attr_config);
>  	video_unregister_device(&uvc->vdev);
>  	v4l2_device_unregister(&uvc->v4l2_dev);