usb: gadget: uvc: default the ctrl request interface offsets

For the userspace it is needed to distinguish between requests for the
control or streaming interface. The userspace would have to parse the
configfs to know which interface index it has to compare the ctrl
requests against. Since the interface numbers are not fixed, e.g. for
composite gadgets, the interface offset depends on the setup.

The kernel has this information when handing over the ctrl request to
the userspace. This patch removes the offset from the interface numbers
and expose the default interface defines in the uapi g_uvc.h.

Signed-off-by: Michael Grzeschik <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/gadget/function/f_uvc.c

···
 
 /* string IDs are assigned dynamically */
 
-#define UVC_STRING_CONTROL_IDX			0
-#define UVC_STRING_STREAMING_IDX		1
-
 static struct usb_string uvc_en_us_strings[] = {
 	/* [UVC_STRING_CONTROL_IDX].s = DYNAMIC, */
 	[UVC_STRING_STREAMING_IDX].s = "Video Streaming",
···
 	struct uvc_device *uvc = to_uvc(f);
 	struct v4l2_event v4l2_event;
 	struct uvc_event *uvc_event = (void *)&v4l2_event.u.data;
+	unsigned int interface = le16_to_cpu(ctrl->wIndex) & 0xff;
+	struct usb_ctrlrequest *mctrl;
 
 	if ((ctrl->bRequestType & USB_TYPE_MASK) != USB_TYPE_CLASS) {
 		uvcg_info(f, "invalid request type\n");
···
 	memset(&v4l2_event, 0, sizeof(v4l2_event));
 	v4l2_event.type = UVC_EVENT_SETUP;
 	memcpy(&uvc_event->req, ctrl, sizeof(uvc_event->req));
+
+	/* check for the interface number, fixup the interface number in
+	 * the ctrl request so the userspace doesn't have to bother with
+	 * offset and configfs parsing
+	 */
+	mctrl = &uvc_event->req;
+	mctrl->wIndex &= ~cpu_to_le16(0xff);
+	if (interface == uvc->streaming_intf)
+		mctrl->wIndex = cpu_to_le16(UVC_STRING_STREAMING_IDX);
+
 	v4l2_event_queue(&uvc->vdev, &v4l2_event);
 
 	return 0;

include/uapi/linux/usb/g_uvc.h

···
 #define UVC_EVENT_DATA			(V4L2_EVENT_PRIVATE_START + 5)
 #define UVC_EVENT_LAST			(V4L2_EVENT_PRIVATE_START + 5)
 
+#define UVC_STRING_CONTROL_IDX			0
+#define UVC_STRING_STREAMING_IDX		1
+
 struct uvc_request_data {
 	__s32 length;
 	__u8 data[60];