linux-kernel - Re: [PATCH 001/001] USB: ftdi_sio: fix endianess of max packet size

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Date:	Thu, 19 Aug 2010 19:01:44 -0400
From:	Stephen Pape <srpape@...il.com>
To:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 001/001] USB: ftdi_sio: fix endianess of max packet size

I guess you're right about it not being used very often on big endian machines.

The original bug report is here: https://dev.openwrt.org/ticket/7365

>From the user's point of view, priv->max_packet_size would get set to
0x0020 instead of 0x0200, so a message would print saying "Setting
MaxPacketSize 2" when it should be 512. After that you couldn't get
any data from the serial port, because priv->max_packet_size is used
in other sections of the code.

-Stephen

On Thu, Aug 19, 2010 at 5:46 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
>
> On Wed, 18 Aug 2010 07:14:37 -0700 (PDT)
> Michael Wileczka <mikewileczka@...oo.com> wrote:
>
> > From: Michael Wileczka <mikewileczka@...oo.com>
> >
> > The USB max packet size (always little-endian) was not being byte swapped on big-endian systems.
> > Created with 2.6.32.16
> > Applicable since [USB: ftdi_sio: fix hi-speed device packet size calculation] approx 2.6.31
> >
> > Signed-off-by: Michael Wileczka <mikewileczka@...oo.com>
> > ---
> > --- a/drivers/usb/serial/ftdi_sio.c
> > +++ b/drivers/usb/serial/ftdi_sio.c
> > @@ -1397,7 +1397,7 @@ static void ftdi_set_max_packet_size(str
> >       }
> >
> >       /* set max packet size based on descriptor */
> > -     priv->max_packet_size = ep_desc->wMaxPacketSize;
> > +     priv->max_packet_size = le16_to_cpu(ep_desc->wMaxPacketSize);
> >
> >       dev_info(&udev->dev, "Setting MaxPacketSize %d\n", priv->max_packet_size);
> >  }
>
> So I guess nobody noticed this because the driver deosn't get used on
> big-endian machines a lot?
>
> What are the user-visible effects of this bug?
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