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

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Message-ID: <4BD5F43E.4090404@draisberghof.de>
Date:	Mon, 26 Apr 2010 22:14:54 +0200
From:	Josua Dietze <digidietze@...isberghof.de>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Michał Nazarewicz <m.nazarewicz@...sung.com>,
	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"

Alan Stern schrieb:

> On Mon, 26 Apr 2010, Josua Dietze wrote:
>> 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.


Important for the Linux handling is that "mode 1" is clearly 
distinguishable from "mode 2", either by using a different product ID 
or by setting a different class for the device or interface 0 (will 
most likely be "8" for the install mode).

And it might be a good idea not to re-use any known ID for the install 
mode, like the 05c6:1000 which my Samsung phone and loads of other 
devices are using.
This makes switch handling complicated (though not impossible).


Josua Dietze
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