pine64-rockpro64: add fancontrol

rk3399's operating temps are -20 to 80°C. It has sensors for CPU and GPU.
The MINSTART/-STOP values are a result of empirical testing.

pine64/rockpro64/default.nix

@@ -6,4 +6,25 @@
     "pcie_rockchip_host"
     "phy_rockchip_pcie"
   ];
+  # control the fan on the rockpro64 (like the one in the NAS case)
+  hardware.fancontrol = {
+    enable = lib.mkDefault true;
+    config = lib.mkDefault ''
+      INTERVAL=3
+      DEVPATH=hwmon0=devices/virtual/thermal/thermal_zone0 hwmon1=devices/virtual/thermal/thermal_zone1 hwmon3=devices/platform/pwm-fan
+      DEVNAME=hwmon0=cpu_thermal hwmon1=gpu_thermal hwmon3=pwmfan
+      # There can only be one sensor mapped to one pwm:
+      # https://github.com/lm-sensors/lm-sensors/issues/228
+      # Therefore you'll have to decide if you want to check CPU or GPU
+      # temps. If you want to use GPU instead, replace hwmon0 with
+      # hwmon1 below.
+      FCTEMPS=hwmon3/pwm1=hwmon0/temp1_input
+      MINTEMP=hwmon3/pwm1=40
+      MAXTEMP=hwmon3/pwm1=80
+      MINSTART=hwmon3/pwm1=35
+      MINSTOP=hwmon3/pwm1=30
+      MINPWM=hwmon3/pwm1=0
+      MAXPWM=hwmon3/pwm1=255
+    '';
+  };
 }