Re: PATCH: usb ehci debug port device gadget

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On Tue, 22 Jun 2010, Greg KH wrote:

> > Does it simply copy bytes from one port over to the other?  At any
> > rate, the EHCI spec doesn't say anything about how a debug device has
> > to work; it only says how the debug port itself works.  That port is
> > theoretically capable of handling any high-speed device, subject to its
> > length limitation (no packet can be longer than 8 bytes).
> > 
> > Is that limitation the reason a special gadget driver is needed?
> The EHCI controller has some type of handshake happening for it to
> determine that this really is a debug device, so that needs to be
> emulated in the gadget somehow.  Because of that, I would assume we need
> some code to do so.

The handshake, if any, is done by the driver and not the controller.  
The EHCI debug-port driver can always be updated to work with a wider 
range of debug devices.

Would it make sense to provide a "debug gadget" module option for 
g_serial instead of creating a separate gadget driver?  Or are the two 
so dissimilar that it wouldn't be worthwhile?

Alan Stern

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