Linux has traditionally been centered around processor performance and power consumption. Thermal management has been a secondary concern - occasionally used for fan speed control, sometimes for processor throttling, and once in a rare while for an emergency thermal shutdown.
Handheld devices change the rules. Skin temperature is a dominant metric, the processor may be a minority player in heat generation, and there are no fans.
This paper describes extensions to Linux thermal management to meet the challenges of handheld devices.