linux-kernel - Re: Writing a driver for a legacy serial device

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Date:	Thu, 21 Jun 2007 11:33:58 +0200
From:	Jean Delvare <khali@...ux-fr.org>
To:	Dmitry Torokhov <dtor@...ightbb.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Vojtech Pavlik <vojtech@....cz>
Subject: Re: Writing a driver for a legacy serial device

Hi Dmitry,

On Wed, 20 Jun 2007 23:11:32 -0400, Dmitry Torokhov wrote:
> On Wednesday 20 June 2007 04:56, Jean Delvare wrote:
> > Ah, I see. There's no way to detect what device is connected to the
> > serial port, so we need a user-space tool to bind the port to the right
> > driver? Makes some sense, even though it's a but strange that I need
> > something called inputattach for a device which isn't an input device.
> 
> Because serio interface is mostly used with input devices. For all other
> devices I think universal answer is "userspace" but with input devices
> we want to do processing in kernel so we can route events into console
> and other standard interfaces (although one coudl use uinput to achieve
> similar result).

OK. This leads me to a question: is it OK for me to add support for my
non-input device to inputattach, or is a separate, dedicated helper
tool preferred? Both ways are fine with me, I don't know what the input
subsystem maintainers expect.

> > But unfortunately, my driver's .connect function is still not called.
> > I guess that I missed one step? Any idea what it would be?
> 
> Not sure. Could you check /sys/bus/serio/devices/serioX/id/* and verify
> that inputattach sets up serio port properly?

Thanks for the hint, I checked that and the proto value was 42 instead
of the expected 40. Reading the source code of my local copy of
inputattach.c, I found that SERIO_RS232 was OR'd to the value. This
seems to be a rather old bug which is already fixed upstream:

http://linuxconsole.cvs.sourceforge.net/linuxconsole/ruby/utils/inputattach.c?r1=1.23&r2=1.24

But for some reason the openSuse package is lagging behind. I'll go
update it.

After fixing this, I finally see my .connect function being called! Now
I can start doing the real driver development work. Thanks a lot for
your highly valuable help, Dmitry :)

-- 
Jean Delvare
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