Great,thanks Alan and David.
Your answers are exactly what I really needed.
Alan,
According to your implication,I took a look at
rh_call_control(),and finally found such piece of code,I felt this
explains my question clearly.
376 case DeviceRequest | USB_REQ_GET_DESCRIPTOR:
377 switch (wValue & 0xff00) {
378 case USB_DT_DEVICE << 8:
379 if (hcd->driver->flags & HCD_USB2)
380 bufp = usb2_rh_dev_descriptor;
381 else if (hcd->driver->flags & HCD_USB11)
382 bufp = usb11_rh_dev_descriptor;
383 else
384 goto error;
385 len = 18;
386 break;
Now my concern is, for root hub, here we can see, hcd->driver->flags
will be used to decide which descriptor will be returned, however,
what if non-root hub?
> If the root hub doesn't operate at high speed then it returns 0. If
> the root hub supports high speed then it returns 1. See
> rh_call_control() in drivers/usb/core/hcd.c.
>
> As far as I know, there are no root hubs with more than one TT.
>
> Alan Stern
>
>
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