USB: Fallback to generic driver when specific driver fails

If ->probe fails for a device specific driver, ask the driver core to
reprobe us, after having flagged the device for the generic driver to be
forced.
Signed-off-by: Bastien Nocera <hadess@hadess.net>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/20191016093933.693-6-hadess@hadess.netSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/driver.c

@@ -270,7 +270,10 @@ static int usb_probe_device(struct device *dev)
 		return error;
 
 	error = udriver->probe(udev);
-	/* TODO: fallback to generic driver in case of error */
+	if (error == -ENODEV && udriver != &usb_generic_driver) {
+		udev->use_generic_driver = 1;
+		return -EPROBE_DEFER;
+	}
 	return error;
 }
 

drivers/usb/core/generic.c

@@ -213,6 +213,9 @@ static int __check_usb_generic(struct device_driver *drv, void *data)
 
 static bool usb_generic_driver_match(struct usb_device *udev)
 {
+	if (udev->use_generic_driver)
+		return true;
+
 	/*
 	 * If any other driver wants the device, leave the device to this other
 	 * driver.

include/linux/usb.h

@@ -708,6 +708,7 @@ struct usb_device {
 	unsigned lpm_disable_count;
 
 	u16 hub_delay;
+	unsigned use_generic_driver:1;
 };
 #define	to_usb_device(d) container_of(d, struct usb_device, dev)