linux-kernel - Re: [PATCH v2] usb: gadget: uvc: allow changing interface name via configfs

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Date:   Sat, 2 Apr 2022 12:24:23 +0100
From:   John Keeping <john@...anate.com>
To:     Dan Vacura <w36195@...orola.com>
Cc:     linux-usb@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Corbet <corbet@....net>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Felipe Balbi <balbi@...nel.org>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Carlos Bilbao <bilbao@...edu>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v2] usb: gadget: uvc: allow changing interface name via
 configfs

On Fri, Apr 01, 2022 at 11:04:45AM -0500, Dan Vacura wrote:
> Add a configfs entry, "function_name", to change the iInterface field
> for VideoControl. This name is used on host devices for user selection,
> useful when multiple cameras are present. The default will remain "UVC
> Camera".

> diff --git a/drivers/usb/gadget/function/f_uvc.c b/drivers/usb/gadget/function/f_uvc.c
> index 71bb5e477dba..50e6e7a58b41 100644
> --- a/drivers/usb/gadget/function/f_uvc.c
> +++ b/drivers/usb/gadget/function/f_uvc.c
> @@ -44,7 +44,7 @@ MODULE_PARM_DESC(trace, "Trace level bitmask");
>  #define UVC_STRING_STREAMING_IDX		1
>  
>  static struct usb_string uvc_en_us_strings[] = {
> -	[UVC_STRING_CONTROL_IDX].s = "UVC Camera",
> +	/* [UVC_STRING_CONTROL_IDX].s = DYNAMIC, */
>  	[UVC_STRING_STREAMING_IDX].s = "Video Streaming",
>  	{  }
>  };
> @@ -676,6 +676,7 @@ uvc_function_bind(struct usb_configuration *c, struct usb_function *f)
>  	uvc_hs_streaming_ep.bEndpointAddress = uvc->video.ep->address;
>  	uvc_ss_streaming_ep.bEndpointAddress = uvc->video.ep->address;
>  
> +	uvc_en_us_strings[UVC_STRING_CONTROL_IDX].s = opts->function_name;
>  	us = usb_gstrings_attach(cdev, uvc_function_strings,
>  				 ARRAY_SIZE(uvc_en_us_strings));
>  	if (IS_ERR(us)) {
> @@ -866,6 +867,7 @@ static struct usb_function_instance *uvc_alloc_inst(void)
>  
>  	opts->streaming_interval = 1;
>  	opts->streaming_maxpacket = 1024;
> +	snprintf(opts->function_name, sizeof(opts->function_name), "UVC Camera");

This only allows a single language to be specified.  I know that's what
the existing string uses, but for other strings which can be set by
userspace multiple languages are supported.

Should we be making USB_CONFIG_STRINGS_LANG more generic so that it can
be used by functions as well as the core configfs code?