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>

diff --git a/common/usb.c b/common/usb.c
index 6cb92ef4f52d8afede9dd94878edde0f95380ef9..88cee810fac1ac88ca7577824fbdf9d07859caca 100644 (file)
--- a/common/usb.c
+++ b/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;
        }