[U-Boot] [PATCH 03/16] usb: Remove unnecessary work in usb_setup_descriptor()

[Bin Meng]

Hi,

On Fri, Jun 23, 2017 at 5:54 PM, Bin Meng <bmeng.cn at gmail.com> wrote:
> The only work we need do in usb_setup_descriptor() is to initialize
> dev->descriptor.bMaxPacketSize0, when do_read is false. Other steps
> are the same as do_read being true.
>
> 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 | 40 ++++++++++++++++++----------------------
>  1 file changed, 18 insertions(+), 22 deletions(-)
>
> diff --git a/common/usb.c b/common/usb.c
> index 15e1e4c..293d968 100644
> --- a/common/usb.c
> +++ b/common/usb.c
> @@ -962,37 +962,33 @@ static int usb_setup_descriptor(struct usb_device *dev, bool do_read)
>          * some more, or keeps on retransmitting the 8 byte header.
>          */
>
> -       if (dev->speed == USB_SPEED_LOW) {
> -               dev->descriptor.bMaxPacketSize0 = 8;
> -               dev->maxpacketsize = PACKET_SIZE_8;
> -       } else {
> -               dev->descriptor.bMaxPacketSize0 = 64;
> -               dev->maxpacketsize = PACKET_SIZE_64;
> -       }
> -       dev->epmaxpacketin[0] = dev->descriptor.bMaxPacketSize0;
> -       dev->epmaxpacketout[0] = dev->descriptor.bMaxPacketSize0;
> -
>         if (do_read) {
>                 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)
>                         return err;
> +       } else {
> +               if (dev->speed == USB_SPEED_LOW)
> +                       dev->descriptor.bMaxPacketSize0 = 8;
> +               else
> +                       dev->descriptor.bMaxPacketSize0 = 64;
>         }
>
>         dev->epmaxpacketin[0] = dev->descriptor.bMaxPacketSize0;
> --

For some reason that I don't understand, this patch breaks EHCI.
dev->maxpacketsize is equal to zero with this patch, which leads to a
'divide error' exception in ehci_submit_async(). Not sure if anyone
has some hints?

For now, I will just drop this patch in v2. This needs be further revisited.

Regards,
Bin