Reported by Nikolaus Schaller, Sep 13, 2019

The basic idea is to read some iio temperature sensor (battery 
monitor or something else close to the battery) and throttle the CPU 
clock (OPPs) so that heat is reduced.

This means adding code to the board file and refer to 
\ {
   thermal-zones {
     battery_thermal: battery_thermal {
	polling-delay-passive = <1000>; /* milliseconds */
	polling-delay = <1000>; /* milliseconds */
	coefficients = <0 20000>;
			/* sensor       ID */
	thermal-sensors = <&some-thermal-sensor 0>;
        };

   battery_trips: trips {
          battery_alert0: cpu_alert {
               temperature = <45000>; /* millicelsius */
               hysteresis = <2000>; /* millicelsius */
               type = "passive";
          };
          battery_crit: cpu_crit {
               temperature = <55000>; /* millicelsius */
               hysteresis = <2000>; /* millicelsius */
               type = "critical";
          };
    };

    battery_cooling_maps: cooling-maps {
      map0 {
           trip = <&battery_alert0>;
           /* do something e.g. turn off charging or reduce 
processor clock */
           cooling-device = <&cpu 0 1>;
      };
   };
};

We may have to map the iio sensor value to the thermal sensors.