USB: cdc-acm: clean up no-union-descriptor handling

For interfaces that lack a union descriptor, probe for a
"combined-interface" before falling back to the call-management
descriptor instead of the other way round.

This allows for the removal of the NO_DATA_INTERFACE quirk and makes the
probe algorithm somewhat easier to follow.
Acked-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20200921135951.24045-5-johan@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/cdc-acm.c

@@ -1219,26 +1219,19 @@ static int acm_probe(struct usb_interface *intf,
 		call_intf_num = cmgmd->bDataInterface;
 
 	if (!union_header) {
-		if (call_intf_num > 0) {
+		if (intf->cur_altsetting->desc.bNumEndpoints == 3) {
+			dev_dbg(&intf->dev, "No union descriptor, assuming single interface\n");
+			combined_interfaces = 1;
+			control_interface = data_interface = intf;
+			goto look_for_collapsed_interface;
+		} else if (call_intf_num > 0) {
 			dev_dbg(&intf->dev, "No union descriptor, using call management descriptor\n");
-			/* quirks for Droids MuIn LCD */
-			if (quirks & NO_DATA_INTERFACE) {
-				data_interface = usb_ifnum_to_if(usb_dev, 0);
-			} else {
-				data_intf_num = call_intf_num;
-				data_interface = usb_ifnum_to_if(usb_dev, data_intf_num);
-			}
+			data_intf_num = call_intf_num;
+			data_interface = usb_ifnum_to_if(usb_dev, data_intf_num);
 			control_interface = intf;
 		} else {
-			if (intf->cur_altsetting->desc.bNumEndpoints != 3) {
-				dev_dbg(&intf->dev,"No union descriptor, giving up\n");
-				return -ENODEV;
-			} else {
-				dev_warn(&intf->dev,"No union descriptor, testing for castrated device\n");
-				combined_interfaces = 1;
-				control_interface = data_interface = intf;
-				goto look_for_collapsed_interface;
-			}
+			dev_dbg(&intf->dev, "No union descriptor, giving up\n");
+			return -ENODEV;
 		}
 	} else {
 		int class = -1;
@@ -1882,11 +1875,6 @@ static const struct usb_device_id acm_ids[] = {
 
 	/* NOTE: non-Nokia COMM/ACM/0xff is likely MSFT RNDIS... NOT a modem! */
 
-	/* Support for Droids MuIn LCD */
-	{ USB_DEVICE(0x04d8, 0x000b),
-	.driver_info = NO_DATA_INTERFACE,
-	},
-
 #if IS_ENABLED(CONFIG_INPUT_IMS_PCU)
 	{ USB_DEVICE(0x04d8, 0x0082),	/* Application mode */
 	.driver_info = IGNORE_DEVICE,

drivers/usb/class/cdc-acm.h

@@ -135,9 +135,8 @@ struct acm {
 #define NO_UNION_NORMAL			BIT(0)
 #define SINGLE_RX_URB			BIT(1)
 #define NO_CAP_LINE			BIT(2)
-#define NO_DATA_INTERFACE		BIT(4)
-#define IGNORE_DEVICE			BIT(5)
-#define QUIRK_CONTROL_LINE_STATE	BIT(6)
-#define CLEAR_HALT_CONDITIONS		BIT(7)
-#define SEND_ZERO_PACKET		BIT(8)
-#define DISABLE_ECHO			BIT(9)
+#define IGNORE_DEVICE			BIT(3)
+#define QUIRK_CONTROL_LINE_STATE	BIT(4)
+#define CLEAR_HALT_CONDITIONS		BIT(5)
+#define SEND_ZERO_PACKET		BIT(6)
+#define DISABLE_ECHO			BIT(7)