Re: [PATCH 3/3] USB: driver for Freescale QUICC Engine USB Host Controller

Sergei Shtylyov
2008-09-24T19:17:18Z

Hello.

David Brownell wrote:

>>>> ... then the root hub emulation is completely pointless.

>>>It isn't. We always should emulate the root hub. The root hub
>>>is part and parcel of any USB Host. Even the one-port one.

>> Hm, maybe that's what USB core thinks (because UHCI/OHCI/EHCI all
>>have it) but e.g. MUSB doesn't have the root hub registers...

> Only the OHCI registers have bit positions matching what the USB
> spec says for hub status bits.

Oh, didn't know that.

> Everything else, including musb_hdrc, has the relevant status encoded in other bits.

Yes, but I thought that if there are no multiple ports, having the hub is
just pointless.

>>I looked at the core and figured that USB core seems to use the root hub
>>interface for port PM, etc. and expects it to bee present, so it seems
>>unavoidable indeed... :-/

> Or more fundamentally: for enumeration. "Unavoidable" is correct. ;)

Not sure what you mean here but I guess having a root hub alows an uniform
model of controlling the ports... anyway, USB specifies that it must be
present in the host.

WBR, Sergei