Re: Researching An Experimental Touchscreen Driver

[Jeremy Moles <jeremy@emperorlinux.com>]

On Wed, 2010-11-24 at 11:07 -0500, Jeremy Moles wrote:
> Hello everyone! I have a piece of hardware here using a vanilla 2.6.34
> kernel (though I can easily change kernels if needed) that has attached
> to it internally a USB touchscreen device. The relevant DMESG info is
> below, and this is printed out whenever the module 'usbhid' is loaded.
> 
> --------------------------------------------------------------------
> 
> usbcore: registered new interface driver hiddev
> input: Fujitsu Component USB Touch Panel
> as /devices/pci0000:00/0000:00:1a.0/usb3/3-2/3-2:1.0/input/input9
> generic-usb 0003:0430:0501.0002: input: USB HID v1.00 Mouse [Fujitsu
> Component USB Touch Panel] on usb-0000:00:1a.0-2/input0
> usbcore: registered new interface driver usbhid
> usbhid: USB HID core driver
> 
> --------------------------------------------------------------------
> 
> For a long time now, we have been successfully configuring these
> machines using the device node created when this driver is loaded, often
> something like /dev/input/event5 (with a UDEV rule to make the name more
> sensible). In X, we've been using the "evtouch" driver with this device
> node, to great effect.
> 
> However, I am doing a bit of research and experimentation, and what I
> would like to do is write some custom driver code to interface with this
> device, instead of letting usbhid manage it. My question is, where is
> the best place to start?
> 
> - Since usbhid already recognizes and binds to this device, what code
> can I begin studying to see exactly how it's detecting this and
> formatting input?
> 
> - Once usbhid attaches to this device, is the device in some kind of
> lock? Is it possible to simply inject additional features or formatting
> functions, possibly via quirks? (I don't quite understand how to do
> anything with quirks other than blacklist a device).
> 
> - If I want to write a full driver for the device, what source file
> would be best to start from? I've tried hacking usbtouchscreen.c and
> hid-ntrig.c for the last few days to try and get them to bind to the
> device, but neither attempt has seen any success. My hid-ntrig change
> refuses to successfully call hid_parse(), and my usbtouchscreen change
> continually returns some error code in the IRQ callback.

I hope this isn't bad etiquette to self-bump my owns posts... I was just
curious if anyone might have any advice. I've continued to hack around,
and I'm certainly gaining more knowledge, but not quite there yet.

Is there a good primer anywhere, or does have any skeleton code they
use, for writing input drivers in Linux? The code is already there in
usbhid.ko for this particular device, so I know it's just a matter of
piecing it together, adding my modifications, and making them play
nice. :)