linux-kernel - Re: [RFC 0/2] USB gadget

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Message-ID: <20120817014609.GB2949@dhcp-172-17-9-228.mtv.corp.google.com>
Date:	Thu, 16 Aug 2012 18:46:31 -0700
From:	Joel Becker <jlbec@...lplan.org>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Andrzej Pietrasiewicz <andrzej.p@...sung.com>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	'Kyungmin Park' <kyungmin.park@...sung.com>,
	'Felipe Balbi' <balbi@...com>,
	'Greg Kroah-Hartman' <gregkh@...uxfoundation.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	'Alan Stern' <stern@...land.harvard.edu>
Subject: Re: [RFC 0/2] USB gadget - configfs

On Thu, Aug 16, 2012 at 03:47:15PM +0200, Sebastian Andrzej Siewior wrote:
> On 08/16/2012 03:17 PM, Andrzej Pietrasiewicz wrote:
> >A lun is "opened" on storing the "file" attribute of the lun, it is in
> >fsg_lun_store_file, storage_common.c. So, again, this is a configfs
> >callback.
> >
> >On storing the connect attribute, the following happens: a composite driver
> >is probed, then all the configurations are iterated over, their functions
> >being bound in turn. After the gadget is set up this way, the host notices
> >connecting a new mass storage device.
> 
> The configuration has to remain unchanged until the "connect" attribute
> is changed (i.e. unconnected). That means the gadget can only be
> reconfigured once it is not active.

	Yes, that's my understanding of the driver code.  What I'm
trying to understand is the trigger for setting connect=1.  See, all of
the other configfs steps you outlined make sense to me as "part of the
gadget's internal state".  While I don't know what C1 and F1 are (I
assume G1 is Gadget1), I don't know that it matters.
	What changes the state to "active"?  That is, what triggers
setting connect=1?  Is it just part of the flow of power-up, or is there
some separation between "setting myself up" and "seeing that a host
wants to talk to me"?

Joel

-- 

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			http://www.jlbec.org/
			jlbec@...lplan.org
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