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

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Message-ID: <4BD81ED5.1050408@draisberghof.de>
Date:	Wed, 28 Apr 2010 13:41:09 +0200
From:	Josua Dietze <digidietze@...isberghof.de>
To:	Michał Nazarewicz <m.nazarewicz@...sung.com>
CC:	Alan Stern <stern@...land.harvard.edu>,
	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"

Michał Nazarewicz schrieb:
> On Mon, 26 Apr 2010 22:14:54 +0200, Josua Dietze 
> <digidietze@...isberghof.de> wrote:
> 
>> 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).
> 
> So it will be enough to change the USB device class for the zeroth
> interface for udev to recognise the mass storage to be ejected?  Note
> that I will use mass storage in the second mode as well.

This is often the case with the common "zero-cd" devices, but 
they have the storage on upper interface numbers after switching.

The point is to enable udev or any other tool to distinguish 
between "unswitched" and "switched"; otherwise the procedure 
for switching will be executed on *both* modes which might 
disturb the device or the system.

A change in one of the attributes like iProduct or iSerial 
could be detected as well of course.

> Also, I think that it might be a good idea to make some "standardised"
> mechanism for all such devices so that a generic udev code could be
> written.  Adding things to the descriptors may be difficult in a way,
> but maybe adding "[NoCD]" to the interface name would be enough.

That is up to the (countless) manufacturers of course; on the 
other hand, the Windows drivers need to recognize the mode as 
well so there should always be one way or the other to 
accomplish that.


Josua Dietze
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