evdev fails with "Couldn't open mtdev device"

[walt]

On 07/11/2011 02:24 AM, Florian Echtler wrote:
> Hi everyone,
> 
> I'm trying to configure a secondary X server for an auxiliary touchscreen,
> but I'm having some problems with the input configuration. To keep input
> for my main screen and the auxiliary screen separate, I'm using the following
> config for the secondary one:
> 
> Section "InputDevice"
>         Identifier "mimoTouch"
>         Driver "evdev"
>         Option "CorePointer" "true"B
>         Option "Device" "/dev/input/event2"
> EndSection

Have you read about the new "InputClass" Section?  It has some advantages
over the older "InputDevice", including the important ability to identify
devices by their plug-n-play names instead the "event" number.

As an example, here's my input section for a non-standard mouse:

#cat /etc/X11/xorg.conf.d/10-trackball.conf 
Section "InputClass"   <--------------- note the new name
        Identifier "trackball"   <----- I made this name up
        MatchProduct "ImExPS"    <----- important: I did not make this up
        Option "AutoServerLayout" "on"
        Option "Emulate3Buttons" "on"
        Option "EmulateWheel" "on"
        Option "EmulateWheelButton" "8"
EndSection

Note the "MatchProduct" keyword.  Unless you have two identical input devices
this product name will be unique and invariant over reboots, unlike "event2".

There are two places I could get the string for MatchProduct -- dmesg and
#udevadm info --export-db:

#dmesg|grep Logitech
input: ImExPS/2 Logitech Explorer Mouse as /devices/platform/i8042/serio1/input/input4

And the corresponding (very small) section from udevadm info --export-db:

P: /devices/platform/i8042/serio1/input/input4
E: UDEV_LOG=3
E: DEVPATH=/devices/platform/i8042/serio1/input/input4
E: PRODUCT=11/2/6/6d
E: NAME="ImExPS/2 Logitech Explorer Mouse"
E: PHYS="isa0060/serio1/input0"
E: PROP=0
E: EV=7
E: KEY=1f0000 0 0 0 0 0 0 0 0
E: REL=143
E: MODALIAS=input:b0011v0002p0006e006D-e0,1,2,k110,111,112,113,114,r0,1,6,8,amlsfw
E: SUBSYSTEM=input

I don't know if any of this will help solve your problem, but I'd be interested
to know if any of the experts here will include it in their advice.