[U-Boot] [PATCH v3 3/3] usb: Early failure when the first descriptor read fails or is invalid

[Stephen Warren]

On 04/04/2015 07:12 AM, Paul Kocialkowski wrote:
> This may happen when using an USB1 device on a controller that only supports
> USB2 (e.g. EHCI). Reading the first descriptor will fail (read 0 byte), so we
> can abort the process at this point instead of failing later and wasting time.

FYI, this patch breaks USB keyboard (or perhaps any USB 1.x device)
support on the RPi.

> diff --git a/common/usb.c b/common/usb.c

> @@ -956,7 +956,7 @@ int usb_new_device(struct usb_device *dev)
>  	 */
>  #ifndef CONFIG_USB_XHCI
>  	err = usb_get_descriptor(dev, USB_DT_DEVICE, 0, desc, 64);
> -	if (err < 0) {
> +	if (err < sizeof(struct usb_device_descriptor)) {
>  		debug("usb_new_device: usb_get_descriptor() failed\n");
>  		return -EIO;
>  	}

The value returned here is 8 not 18 (the sizeof the descriptor), so the
code bails out with an error.

Given the description of what this patch is attempting to achieve,
shouldn't the replacement check be:

	if (err <= 0) {

My guess for why the value 8 is returned is because the device's
maxpacket is 8, and the DWC2 driver only attempts to transfer 1 packet
because the requested transfer size is 64, and the default packet size
is 64, which means 1 packet. Note that DWC2 HW (perhaps unlike e.g.
EHCI) requires the driver to specify the number of packets transferred,
not a byte count. However, I haven't validated that yet. My device is a
USB 1.x FS keyboard.