Change the FAN_TACH pin to other gpio

I have used GPIO8 for SD Detect,and assigned FAN_TACH to PIN228, I have changed the device tree and enabled the SDMMC3,when i set the pwm PWM_duty_cycle and the fan worked well,but can not get the fan speed

cat /sys/devices/generic_pwm_tachometer/hwmon/hwmon1/rpm

it alwys get 0.

i can not find any info about gpio_tachometer:

 Device tree bindings for fan tach output connected to IRQ capable GPIO.
   Required properties:
   - compatible    : "nvidia,gpio-tachometer"
   - win-len       : Duration in multiples of 100ms, for which the IRQ will be enabled
                     while measuring speed. Maximum allowed value is 5 seconds to avoid
                     possible IRQ overload at high speed.
   - pulse-per-rev : Number of signals generated on the tach output pin by the motor
                     for one full rotation.
  - gpio          : GPIO pin on which tach output of the motor is connected.
  Optional properties:
  - schedule-delay: Time in milliseconds for the background thread to monitor the speed.
                    If the measured speed is 0, system shutdown will be initiated.
                    Time duration should be higher than win-len time.
          gpio_tachometer {
                  compatible = "nvidia,gpio-tachometer";
                  win-len = <2>;                  /*For every measurement, take samples for 200ms*/
                  pulse-per-rev = <2>;            /*Motor generates 2 pulses for every full rotation*/
                  schedule-delay = <10000>;       /*Check motor speed every 10seconds and shutdown if motor is stopped*/
                  gpio = <&tegra_main_gpio TEGRA_MAIN_GPIO(Y, 1) 0>;
                  status = "okay";


Correct my comment. For xavier, only GPIO08 could be used as fan tach pin.

Thanks for your reply,i got it.