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

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Date:	Wed, 24 Sep 2008 23:17:55 +0400
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	David Brownell <david-b@...bell.net>
Cc:	avorontsov@...mvista.com,
	Andrew Morton <akpm@...ux-foundation.org>, greg@...ah.com,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...abs.org, leoli@...escale.com, timur@...escale.com
Subject: Re: [PATCH 3/3] USB: driver for Freescale QUICC Engine USB Host Controller

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
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