kernel driver gpio-tachometer: =================================== To measure cpu fan/motor speed using GPIO pin, this driver can be used. The driver does not rely on any specific peripheral like input capture. Author: Vishruth Jain Description: ------------ In platforms where the motor speed input pin is NOT connected to input capture pin or any other peripheral capable of measuring the frequency of external signal, this driver can be used to measure motor speed. The driver works by using GPIO IRQ. Driver makes following assumptions: -> The pin to which is motor tach output is connected is IRQ capable. -> Motor speed indicator(tachometer output from motor) has default state high and is pulled to ground level, 1 or more times for every full rotation. Speed is calculated based on the number of times GPIO IRQ is triggered in a time window. Speed in RPM(rotations per minute) is derived from the count captured using IRQ. Optionally driver supports creating a delayed worker, which monitors the motor speed periodically. If the motor is stopped, indicated by speed being 0, the delayed worker initiates system shutdown.