usb: Only get 64 bytes device descriptor for full speed devices

Full speed device endpoint 0 can have 8/16/32/64 bMaxPacketSize0.
Other speed devices report fixed value per USB spec. So it only
makes sense if we send a get device descriptor with 64 bytes to
full speed devices.

While we are here, update the comment block to be within 80 cols.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>

common/usb.c

@@ -970,23 +970,24 @@ static int usb_setup_descriptor(struct usb_device *dev, bool do_read)
 	dev->epmaxpacketin[0] = dev->descriptor.bMaxPacketSize0;
 	dev->epmaxpacketout[0] = dev->descriptor.bMaxPacketSize0;
 
-	if (do_read) {
+	if (do_read && dev->speed == USB_SPEED_FULL) {
 		int err;
 
 		/*
-		 * Validate we've received only at least 8 bytes, not that we've
-		 * received the entire descriptor. The reasoning is:
-		 * - The code only uses fields in the first 8 bytes, so that's all we
-		 *   need to have fetched at this stage.
-		 * - The smallest maxpacket size is 8 bytes. Before we know the actual
-		 *   maxpacket the device uses, the USB controller may only accept a
-		 *   single packet. Consequently we are only guaranteed to receive 1
-		 *   packet (at least 8 bytes) even in a non-error case.
+		 * Validate we've received only at least 8 bytes, not that
+		 * we've received the entire descriptor. The reasoning is:
+		 * - The code only uses fields in the first 8 bytes, so
+		 *   that's all we need to have fetched at this stage.
+		 * - The smallest maxpacket size is 8 bytes. Before we know
+		 *   the actual maxpacket the device uses, the USB controller
+		 *   may only accept a single packet. Consequently we are only
+		 *   guaranteed to receive 1 packet (at least 8 bytes) even in
+		 *   a non-error case.
 		 *
-		 * At least the DWC2 controller needs to be programmed with the number
-		 * of packets in addition to the number of bytes. A request for 64
-		 * bytes of data with the maxpacket guessed as 64 (above) yields a
-		 * request for 1 packet.
+		 * At least the DWC2 controller needs to be programmed with
+		 * the number of packets in addition to the number of bytes.
+		 * A request for 64 bytes of data with the maxpacket guessed
+		 * as 64 (above) yields a request for 1 packet.
 		 */
 		err = get_descriptor_len(dev, 64, 8);
 		if (err)
@@ -1009,7 +1010,7 @@ static int usb_setup_descriptor(struct usb_device *dev, bool do_read)
 		dev->maxpacketsize = PACKET_SIZE_64;
 		break;
 	default:
-		printf("usb_new_device: invalid max packet size\n");
+		printf("%s: invalid max packet size\n", __func__);
 		return -EIO;
 	}