Refactoring the acpi handling code of the N900 to work with all devices

Motivation

I've thought about switching speakers/headphones automatically with audio jack detection as part of my N900 music player project. This is possible by catching acpi events. But I want it to work on all devices, so some refactoring needs to take place first.

Current acpi-related code for the N900

The device-nokia-n900 package sets up busybox' acpid with a custom acpi.map and acpi_handler.sh, when certain acpi events are coming in. So far it turns the keyboard backlight LEDs on and off, when the keyboard gets slided out or back in. The acpi_handler.sh looks like this:

...
case $cmd in
    KP_SLIDE_OPEN)
        adjust_keypad_bl 255    
        ;;
    KP_SLIDE_CLOSE)
        adjust_keypad_bl 0
        ;;
    CAM_BTN_DWN)
        echo "Not implemented yet"
        ;;
...

The acpi.map looks like that:

...
"EV_SW" 0x05 "SW_KEYPAD_SLIDE" 10 1 KP_SLIDE_OPEN
"EV_SW" 0x05 "SW_KEYPAD_SLIDE" 10 0 KP_SLIDE_CLOSE
...

Making it work for all devices

• create a nokia-n900-keypad-blacklight script as derivative from its current acpi_handler.sh. (I think all new device specific scripts should start with the device name if possible.)
• extend the N900's deviceinfo with:

deviceinfo_acpi_slide_open="nokia-n900-keypad-blacklight 255"
deviceinfo_acpi_slide_close="nokia-n900-keypad-blacklight 0"

• install the acpi daemon as dependency of postmarketos-base instead of device-nokia-n900
• put acpi_handler.sh script in postmarketos-base instead of device-nokia-n900
• rewrite acpi_handler.sh: source /etc/deviceinfo and run the deviceinfo_acpi_* commands

When we have that, we can also do generic actions in acpi_handler.sh, such as turning the volume up with alsactl when pressing the volume up button (so this would not require a deviceinfo_acpi_* variable filled out).