media: uvcvideo: Use heuristic to find stream entity

Some devices, like the Grandstream GUV3100 webcam, have an invalid UVC
descriptor where multiple entities share the same ID, this is invalid
and makes it impossible to make a proper entity tree without heuristics.

We have recently introduced a change in the way that we handle invalid
entities that has caused a regression on broken devices.

Implement a new heuristic to handle these devices properly.

Reported-by: Angel4005 <[e-mail]>
Closes: https://lore.kernel.org/linux-media/CAOzBiVuS7ygUjjhCbyWg-KiNx+HFTYnqH5+GJhd6cYsNLT=[e-mail]/
Fixes: 0e2ee70291e6 ("media: uvcvideo: Mark invalid entities with id UVC_INVALID_ENTITY_ID")
Cc: [e-mail]
Signed-off-by: Ricardo Ribalda <[e-mail]>
Reviewed-by: Hans de Goede <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>

drivers/media/usb/uvc/uvc_driver.c

···
 
 static struct uvc_streaming *uvc_stream_by_id(struct uvc_device *dev, int id)
 {
-	struct uvc_streaming *stream;
+	struct uvc_streaming *stream, *last_stream;
+	unsigned int count = 0;
 
 	list_for_each_entry(stream, &dev->streams, list) {
+		count += 1;
+		last_stream = stream;
 		if (stream->header.bTerminalLink == id)
 			return stream;
+	}
+
+	/*
+	 * If the streaming entity is referenced by an invalid ID, notify the
+	 * user and use heuristics to guess the correct entity.
+	 */
+	if (count == 1 && id == UVC_INVALID_ENTITY_ID) {
+		dev_warn(&dev->intf->dev,
+			 "UVC non compliance: Invalid USB header. The streaming entity has an invalid ID, guessing the correct one.");
+		return last_stream;
 	}
 
 	return NULL;