[U-Boot] [PATCH 06/14] usb: Only get 64 bytes device descriptor for full speed devices

[Stefan Roese]

On 18.09.2017 15:40, Bin Meng wrote:
> 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 at gmail.com>
> ---
> 
>   common/usb.c | 29 +++++++++++++++--------------
>   1 file changed, 15 insertions(+), 14 deletions(-)
> 
> diff --git a/common/usb.c b/common/usb.c
> index 6cb92ef..88cee81 100644
> --- 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;
>   	}
>   
> 

Reviewed-by: Stefan Roese <sr at denx.de>
Tested-by: Stefan Roese <sr at denx.de>

Thanks,
Stefan