linux-kernel - Re: [PATCH 0/2] Add a skeleton module to perform a basic initialization on certain USB devices

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Message-ID: <6032606.IBdJ88hxWq@the-raza>
Date:	Sat, 23 Jan 2016 16:56:27 +0100
From:	Michal Malý <madcatxster@...oid-pointer.net>
To:	Bjørn Mork <bjorn@...k.no>
Cc:	gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, dmitry.torokhov@...il.com,
	jikos@...nel.org, elias.vds@...il.com, edwin@...ds.nl,
	simon@...gewell.org
Subject: Re: [PATCH 0/2] Add a skeleton module to perform a basic initialization on certain USB devices

On sobota 23. ledna 2016 13:46:32 CET Bjørn Mork wrote:
> Michal Malý <madcatxster@...oid-pointer.net> writes:
> > This mini series adds a simple skeleton module whose only purpose is to
> > bring devices that at first appear as a generic USB device into another
> > mode that can be handled by a more specific subsystem.
> > 
> > This patch was originally requested by Dmitry, reasoning that loading the
> > entire xpad module just to switch a Logitech G920 wheel into HID mode is
> > excessive and does not make much sense.
> > 
> > The module can be extended to handle any other USB device that might
> > require such a switch.
> 
> Can this switching be done in userspace? That's what we normally do, ref
> usb_modeswitch.

I briefly considered leaving the switch up to the userspace and handling the 
device in the kernel only once it's been switched. I am however uncertain how 
to advertise this to the users. Writing a tiny app that would currently handle 
just one device seems like an overkill, abusing usb_modeswitch seems counter-
intuitive as it's purpose is to handle various USB modems. Having a tiny 
module in the kernel looks like the most straightforward thing to do as far as 
user experience is concerned.

I would not object to deferring the switch to userspace as long as there is an 
easy way how to communicate the need for a small switching tool to the users.

Michal