USB: musb: use right poll limit for low speed devices

Remove wrongly applied upper limit on the interrupt transfer
interval for low speed devices (not much of an error per se,
according to USB specs).
Signed-off-by: NSergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/usb/musb/musb_host.c

@@ -1863,19 +1863,21 @@ static int musb_urb_enqueue(
 	}
 	qh->type_reg = type_reg;
 
-	/* precompute rxinterval/txinterval register */
-	interval = min((u8)16, epd->bInterval);	/* log encoding */
+	/* Precompute RXINTERVAL/TXINTERVAL register */
 	switch (qh->type) {
 	case USB_ENDPOINT_XFER_INT:
-		/* fullspeed uses linear encoding */
-		if (USB_SPEED_FULL == urb->dev->speed) {
-			interval = epd->bInterval;
-			if (!interval)
-				interval = 1;
+		/*
+		 * Full/low speeds use the  linear encoding,
+		 * high speed uses the logarithmic encoding.
+		 */
+		if (urb->dev->speed <= USB_SPEED_FULL) {
+			interval = max_t(u8, epd->bInterval, 1);
+			break;
 		}
 		/* FALLTHROUGH */
 	case USB_ENDPOINT_XFER_ISOC:
-		/* iso always uses log encoding */
+		/* ISO always uses logarithmic encoding */
+		interval = min_t(u8, epd->bInterval, 16);
 		break;
 	default:
 		/* REVISIT we actually want to use NAK limits, hinting to the