Bluetooth: btusb: Dynamic alternate setting

The alternate setting must be dynamically set according to the number of
active SCO links, and the bit depth of the audio. The possible values
for the alternate setting are described in the Bluetooth Core
Specification, Volume 4, Part B, section 2.1.1.
Signed-off-by: Mikel Astiz <mikel.astiz.oss@gmail.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo Padovan <gustavo@padovan.org>

drivers/bluetooth/btusb.c

@@ -855,6 +855,7 @@ static void btusb_work(struct work_struct *work)
 {
 	struct btusb_data *data = container_of(work, struct btusb_data, work);
 	struct hci_dev *hdev = data->hdev;
+	int new_alts;
 	int err;
 
 	if (hdev->conn_hash.sco_num > 0) {
@@ -868,11 +869,19 @@ static void btusb_work(struct work_struct *work)
 
 			set_bit(BTUSB_DID_ISO_RESUME, &data->flags);
 		}
-		if (data->isoc_altsetting != 2) {
+
+		if (hdev->voice_setting & 0x0020) {
+			static const int alts[3] = { 2, 4, 5 };
+			new_alts = alts[hdev->conn_hash.sco_num - 1];
+		} else {
+			new_alts = hdev->conn_hash.sco_num;
+		}
+
+		if (data->isoc_altsetting != new_alts) {
 			clear_bit(BTUSB_ISOC_RUNNING, &data->flags);
 			usb_kill_anchored_urbs(&data->isoc_anchor);
 
-			if (__set_isoc_interface(hdev, 2) < 0)
+			if (__set_isoc_interface(hdev, new_alts) < 0)
 				return;
 		}