usb: xhci-mtk: add a function to get bandwidth boundary

This is used to simplify unit test.
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Link: https://lore.kernel.org/r/805b3ba66c2f02a52de4440212519aaa58463039.1615170625.git.chunfeng.yun@mediatek.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/xhci-mtk-sch.c

@@ -37,6 +37,25 @@ static int is_fs_or_ls(enum usb_device_speed speed)
 	return speed == USB_SPEED_FULL || speed == USB_SPEED_LOW;
 }
 
+static u32 get_bw_boundary(enum usb_device_speed speed)
+{
+	u32 boundary;
+
+	switch (speed) {
+	case USB_SPEED_SUPER_PLUS:
+		boundary = SSP_BW_BOUNDARY;
+		break;
+	case USB_SPEED_SUPER:
+		boundary = SS_BW_BOUNDARY;
+		break;
+	default:
+		boundary = HS_BW_BOUNDARY;
+		break;
+	}
+
+	return boundary;
+}
+
 /*
 * get the index of bandwidth domains array which @ep belongs to.
 *
@@ -579,13 +598,7 @@ static int check_sch_bw(struct usb_device *udev,
 			break;
 	}
 
-	if (udev->speed == USB_SPEED_SUPER_PLUS)
-		bw_boundary = SSP_BW_BOUNDARY;
-	else if (udev->speed == USB_SPEED_SUPER)
-		bw_boundary = SS_BW_BOUNDARY;
-	else
-		bw_boundary = HS_BW_BOUNDARY;
-
+	bw_boundary = get_bw_boundary(udev->speed);
 	/* check bandwidth */
 	if (min_bw > bw_boundary)
 		return -ERANGE;