Button driver it's common driver for all kinds of buttons.
This driver has its own device tree structure:

buttons{
      	compatible = "brcm,buttons";
   	reset_button {
			ext_irq = <&bca_extintr 54 BCA_GPIO_ACTIVE_LOW (BCA_EXTINTR_TYPE_LOW_LEVEL | BCA_EXTINTR_TYPE_SENSE_EDGE)>;
			press {
   			print = "Button Press -- Hold for 5s to do restore to default";
   		};
			hold {
	  			rst_to_dflt = <5>;
 			};
			release {
  				reset = <0>;
			};	
  		};
		ses_button {
			ext_irq = <&bca_extintr 53 BCA_GPIO_ACTIVE_LOW (BCA_EXTINTR_TYPE_LOW_LEVEL | BCA_EXTINTR_TYPE_SENSE_EDGE)>;
			release {
  				ses = <1>;
			};
		};
};

Name of main node can be any, it's not predefined. In our case it's "buttons". Name of buttons nodes is user defined ("reset_button", "ses_button").
When user build its own button node in DT he must define external interrupt entry. How to define this entry user needs to read bca_extintr_bindingd.txt.
But name of external interrupt entry predefined as "ext_irq". It must be same for each button. Each event/trigger that can happen on button must be defined
as node with predefined name "press", "hold", "release". In each trigger/event node, user must define action property (user defined name). Properties values
can be only timeout (in seconds). "print" action defined and registered by button driver. "print_uboot" action can also be added for u-boot if user needs a
different message. Also for u-boot only,  <action_name>_cmd string property can be used to specify a customized command to run for that action. 

Button driver has external api function for buttons actions hooks registration:

int register_button_action(const char *button_name, char *action_name, buttonNotifyHook_t hook);

For example there is reset button driver. 
It defines two action and hooks:
	- reset (timeout 0, release event)
   - reset to default (timeout 5 sec, hold event)

Third action is print (already registered by button driver).

This id for instance how reset_button driver calls api function for button action hook registration:

register_button_action("reset_button", "rst_to_dflt", btn_hook_rst_to_dflt);
register_button_action("reset_button", "reset", btn_hook_reset);

The Button driver also supports the "gpio-keys" like behavior.
It could send the EV_KEY <linux key code> Press/Released event to userspace. That could be handled via /dev/input/eventX
In order to turn this on the reqiered button should be extended with linux,code=<KEY_CODE>; property and press/release
action should be extended with linux,press and linux,release properies with possible delayed report. The delay is in
miliseconds.
The definitions of the key_codes should be taken from dt-bindings/input/linux-event-codes.h

Ex:
#include <dt-bindings/input/linux-event-codes.h>

test_button {
    ext_irq = <&bca_extintr 53 BCA_GPIO_ACTIVE_LOW (BCA_EXTINTR_TYPE_LOW_LEVEL | BCA_EXTINTR_TYPE_SENSE_EDGE)>;
    linux,code = <KEY_F12>;

    press {
        linux,press = <0>;
    };
    hold {
        linux,release = <20>; /* ms  Send release command if button remain pressed for specified timeout in ms 
                               */
    };
    release {
        linux,release = <0>;
    };
};