STM32 USB support

[Andrew Lunn]

> >> There is a significant difference from the other USB drivers which I
> >> should probably flag up (and document).  The endpoint configuration is
> >> generated dynamically from the USB descriptors.  This gives a lot of
> >> flexibility and potentially allows support for multiple configurations
> >> (untested!).  However, the downside is that I had to leave out devtab
> >> support since the devtab entries need to be set statically.
> >>   
> > Don't you think it's possible to have both options? I haven't looked at
> > the USB subsystem or any drivers, but I think a public driver should
> > behave as the subsystem intends. Maybe the subsystem could be extended
> > for more dynamic usage though.
> 
> The official docs say "To support this the device driver can provide a
> devtab entry for each endpoint".  I took that to mean that devtab
> support was optional - and the dynamic endpoint configuration is a much
> more useful feature IMHO.
> 
> Previously supported hardware has had fixed endpoint configurations
> which makes the static devtab entries easy to implement.  However, with
> dynamic endpoint configuration, the low-level driver doesn't know
> a-priori what endpoints to generate devtab entries for - and nor should it!

The AT91 USB driver has something similar to this. It can configure
the endpoints by looking at the USB descriptors.

I don't remember how it works with respect to devtab entries.

  Andrew