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

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Message-ID: <48DA1544.5010307@ru.mvista.com>
Date:	Wed, 24 Sep 2008 14:24:04 +0400
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	avorontsov@...mvista.com
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	dbrownell@...rs.sourceforge.net, 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.

Anton Vorontsov wrote:
>>>>>> This controller does not integrate the root hub, so this driver also
>>>>>> fakes one-port hub. External hub is required to support more than
>>>>>> one device.
>>>>>>
>>>>>> ...
>>>>>>
>>>>>>       
>>>>>>             
>>>>> Please, no.
>>>>>     
>>>>>           
>>>> What exactly 'no'? ;-)
>>>>   
>>>>         
>>>   No one-port hubs I guess -- they are pointless. Though e.g. MUSB  
>>> driver creates one -- I guess to impersonate a transaction translating  
>>> high-speed hub...
>>>
>>>       
>>   ... 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...
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... :-/

WBR, Sergei


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