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Date: Tue, 24 Apr 2012 23:58:43 +0800
From: Wang YanQing <udknight@gmail.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Anil Nair <anilcoll90@gmail.com>, Greg KH <greg@kroah.com>,
        lkml <linux-kernel@vger.kernel.org>, linux-usb@vger.kernel.org
Subject: Re: [RFC]Is usb port number fixed?
Message-ID: <20120424155843.GA3804@udknight>
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	Alan Stern <stern@rowland.harvard.edu>,
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On Tue, Apr 24, 2012 at 10:14:05AM -0400, Alan Stern wrote:
> In drivers/usb/core/hub.c, look through the hub_events() routine.  
> There are several function calls similar to this one:
> 
> 			ret = hub_port_status(hub, i,
> 					&portstatus, &portchange);
> 
> Here i is the port number.  This asks the hub to send back status and 
> change information for port i.  (See also the code for the 
> hub_port_status() and get_port_status() routines.)

Thanks, I get it.

On Tue, Apr 24, 2012 at 07:52:44PM +0530, anil wrote:
> The USB specification Table 11-13 describes the hub descriptor in
> detail.
> The following data structure struct usb_hub_descriptor defined in
> "drivers/usb/core/hub.h" of Linux  Kernel source contains information
> about the hub descriptor,
> 
>                       struct usb_hub_descriptor {
>                             _u8 bDescLength;
>                           _u8 bDescriptorType;
>                              _u8 bNbrPorts;
>                        _le16 wHubCharacteristics;
>                           _u8 bPwrOn2PwrGood;
>                          _u8 bHubContrCurrent;
>                                    }
> 
> The bNbrPorts  member contains information on the number of
> downstream-facing ports the hub supports. The structure which i have
> provided is in reference to Linux Kernel Version 2.6 series for Linux
> Kernel Version 3.0+, Please consult an expert.
>   	Is this information you wanted?
> 

Yes, It is want I wanted.But maybe "11.5.3.1 Labeling" show more footprint.

Thanks, all guys.
All you give me a very good explanation about the sentence below:

"High quality support from experts available instantly over the Internet at
no charge has played a major role in stitching together a huge Linux community"

which come from the <<Essential Linux Device Drivers>>.

Cheers.

Udknight