linux-kernel - Re: USB gadget with drivers "on board"

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Date:	Mon, 26 Apr 2010 15:34:22 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	MichaÅ Nazarewicz <m.nazarewicz@...sung.com>
cc:	Josua Dietze <digidietze@...isberghof.de>,
	Daniel Mack <daniel@...aq.de>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>,
	Kyungmin Park <kyungmin.park@...sung.com>
Subject: Re: USB gadget with drivers "on board"

On Mon, 26 Apr 2010, Josua Dietze wrote:

> MichaÅ Nazarewicz schrieb:
> 
> > On Mon, 26 Apr 2010 16:16:05 +0200, Daniel Mack <daniel@...aq.de> wrote:
> >> Are you sure they don't do exactly that by running two interfaces in
> >> the same configuration?
> > 
> > Yes, I'm sure.  I've investigated an USB GSM modem which, when plugged
> > for the first time reports as mass storage (single configuration, single
> > interface) and when drivers are installed as a full blown composite
> > gadget.  I still haven't figured out how it does that.
> 
> 
> These are the notorious mode switching devices. In Windows, they 
> obviously install a special storage driver doing one specific action 
> on each following plugging.
> This action - some storage or control command - will "flip" the 
> device, making it "disconnect" and returning as a completely different 
> composite device.
> 
> Storage commands used for this procedure range from "SCSI rezero" over 
> "passthrough" to "SCSI eject", or involve vendor specific stuff.

I was going to say the same thing.  For ease of use, I recommend using
a "SCSI eject" to trigger the mode change.  That way, Linux users who
don't have the usb-modeswitch program installed can get the same effect
by running eject.

Alan Stern

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