Legacy serial device driver - serio/inputattach vs. ldisc vs. userspace daemon

[Rolf Offermanns]

Hello Mentors!
I am about to write a driver for a self-made serial device and would
like to have some opinions about the best way to do it. It is basically
a microcontroler (atmel based) attached to the serial port which has
multiple functions "behind" it.

The setup looks like this:

RS232 <-> Microcontroler <---> Touchpanel
                           +-> Some button keys
                           +-> Temp. sensor
                           +-> You name it

The Atmel multiplexes the single functions on one serial line and now
it's my turn to demultiplex them again an the Linux side.

I would like to have an input event device for the touchpanel (and maybe
the keys) and character devices for the other stuff (temprature sensor).

I browsed the mailinglists and googled a bit and came it with three way
to tackle this:

1. serio driver, like some serial touchpanels use together with
"inputattach".

2. Line discipline. I have not read much about this, but it was
mentioned as a possible solution in another thread on LKML for a legacy
serial device. (http://lkml.org/lkml/2007/6/19/254)

3. A userspace daemon which sits on /dev/ttyS0 and distributes the data
to muliple ptys.


Am I on the right track? Which option is the best in your opinion?

Any help is appreciated.

Thanks,
Rolf