On Mon, 2 Jul 2007, jidong xiao wrote:
> Another separate issue,still focus on this piece of code,(inside
> drivers/usb/core/hub.c, hub_configure())
>
> > >
> > > 570 switch (hdev->descriptor.bDeviceProtocol) {
> > > 571 case 0:
> > > 572 break;
> > > 573 case 1:
> > > 574 dev_dbg(hub_dev, "Single TT\n");
> > > 575 hub->tt.hub = hdev;
> > > 576 break;
> > > 577 case 2:
> > > 578 ret = usb_set_interface(hdev, 0, 1);
> > > 579 if (ret == 0) {
> > > 580 dev_dbg(hub_dev, "TT per port\n");
> > > 581 hub->tt.multi = 1;
> > > 582 } else
> > > 583 dev_err(hub_dev, "Using single
> > > TT (err %d)\n",
> > > 584 ret);
> > > ...
>
> see case 2,note that usb_set_interface() is called,I don't understand
> the purpose of calling this function,you know,based on usb spec 2.0,
> Table 11-14, "hubs are allowed to support only one interface",thus
> neither GET_INTERFACE nor SET_INTERFACE is supported by hubs,or say,
> undefined.So I also looked through the internal part of
> usb_set_interface,maybe we actually won't send any request to the
> hub,but why we call this function at this situation.
Hubs can have only one interface, but that interface can have two
different altsettings. See section 11.23.1 of the spec and see the
revised version of Table 11-14 in the USB 2.0 Errata document.
Alan Stern
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