linux/Documentation/acpi-hotkey.txt

driver/acpi/hotkey.c implement:
1. /proc/acpi/hotkey/event_config 
(event based hotkey or event config interface):
a. add a  event based hotkey(event) : 
echo "0:bus::action:method:num:num" > event_config

b. delete a event based hotkey(event): 
echo "1:::::num:num" > event_config

c.  modify a event based hotkey(event):    
echo "2:bus::action:method:num:num" > event_config

2. /proc/acpi/hotkey/poll_config 
(polling based hotkey or event config interface):
a.add a polling based hotkey(event) : 	
echo "0:bus:method:action:method:num" > poll_config
this adding command will create a proc file 
/proc/acpi/hotkey/method, which is used to get 
result of polling.

b.delete a polling based hotkey(event): 	
echo "1:::::num" > event_config

c.modify a polling based hotkey(event):    
echo "2:bus:method:action:method:num" > poll_config

3./proc/acpi/hotkey/action 
(interface to call aml method associated with a 
specific hotkey(event))
echo "event_num:event_type:event_argument" > 
	/proc/acpi/hotkey/action.
The result of the execution of this aml method is 
attached to /proc/acpi/hotkey/poll_method, which is dnyamically
created.  Please use command "cat /proc/acpi/hotkey/polling_method" 
to retrieve it.

Note: Use cmdline "acpi_generic_hotkey" to over-ride
platform-specific with generic driver.