Re: [PATCH] USB: Fix up bogus bInterval values in endpoint descriptors

On Sunday 10 June 2007, Alan Stern wrote:
> On Sun, 10 Jun 2007, Laurent Pinchart wrote:
> > From my experience, a common cause of bogus bInterval values is
> > developers forgetting that the value has a different meaning for
> > high-speed and low-speed/full-speed devices. I've come across a device
> > reporting interrupt bInterval set to 32 instead of 9. By sheer luck your
> > patch fixes this properly, but it would set a wrong bInterval value for
> > devices setting bInterval to 16 instead of 8 for instance.
> >
> > The USB developers FAQ (available at http://www.lvr.com/usbfaq.htm)
> > states that
> >
> > "Reports are that many device manufacturers are using full-speed
> > bInterval values in high-speed descriptors. Reports also say that under
> > Windows, a device may receive its intended polling rate (rather than its
> > requested polling rate) in spite of this error. Other operating systems
> > are likely to attempt to provide the requested polling rate, or may
> > report an illegal bInterval value."
> >
> > For high-speed interrupt endpoints, wouldn't it be better to set
> > bInterval to fls(bInterval*8) if the requested value is higher than 16 ?
>
> It's okay with me if you want to change the patch in that way.  Just be
> sure to do the conversion correctly.

I prepared a modified patch to handle low/full-speed interrupt bInterval 
values for high-speed devices.

I'll sign and send the patch, but I don't want to take credit for your work. 
Please let me know if I should resend it with different options/comments.

Laurent Pinchart

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