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SubjectRe: [PATCHv3 2/4] usb: gadget: replace "is_dualspeed" with "max_speed"
Hi,

On Tue, Aug 23, 2011 at 04:49:37PM -0400, Alan Stern wrote:
> On Tue, 23 Aug 2011, Michal Nazarewicz wrote:
>
> > On Tue, 23 Aug 2011 20:00:25 +0200, Alan Stern <stern@rowland.harvard.edu>
> > wrote:
> > > For the time being, perhaps the best answer is to use the _lowest_
> > > max_speed value among all the function drivers. It's the simplest
> > > answer and most likely to be correct most of the time.
> >
> > In theory, one could create a composite function with only SS/HS
> > descriptors.
>
> The only reason for doing that would be if the function was incapable
> of carrying out its duties when running at full speed (insufficient
> bandwidth, for example). Something like this is discussed briefly in
> section 9.2.6.6 of the USB-2 spec.
>
> > So it would work for SS/HS but not for FS. I'm not
> > saying that it would make sense (or that it's not a bug) but that
> > adds to the discussion.
>
> If somebody writes a composite gadget containing two functions, one of
> which supports only full speed and the other only high speed, they'll
> get what they deserve. :-)
>
> Still, maybe I was wrong. Maybe it would be better to use the fastest
> speed supported by at least one of the function drivers. The user can
> always force a SuperSpeed-capable device to run at high speed by using
> a USB-2 cable to plug it in. I'm not sure whether the user could force
> such a device to run at full speed, however.

plug it behind a full speed hub, like those that usually come on USB
keyboards.

--
balbi
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