From 4a2be174938ac115beac4f07fa8b7ee33406cde8 Mon Sep 17 00:00:00 2001
From: Paul <paulenuta@users.noreply.github.com>
Date: Thu, 11 Oct 2018 12:17:20 +0300
Subject: [PATCH] Update gpio-fan-overlay.dts (#2711)

Add references, links, clear details, some typo correction.
---
 .../boot/dts/overlays/gpio-fan-overlay.dts    | 36 +++++++++++--------
 1 file changed, 22 insertions(+), 14 deletions(-)

--- a/arch/arm/boot/dts/overlays/gpio-fan-overlay.dts
+++ b/arch/arm/boot/dts/overlays/gpio-fan-overlay.dts
@@ -1,29 +1,37 @@
 /*
  * Overlay for the Raspberry Pi GPIO Fan @ BCM GPIO12.
+ * References: 
+ *	- https://www.raspberrypi.org/forums/viewtopic.php?f=107&p=1367135#p1365084
+ *
  * Optional parameters:
- *	- "gpiopin"	- default GPIO12
- * 	- "temp"	- default 55000
+ *	- "gpiopin"	- BCM number of the pin driving the fan, default 12 (GPIO12);
+ * 	- "temp"	- CPU temperature at which fan is started in millicelsius, default 55000;
+ *
  * Requires:
- *	- kernel configurations: CONFIG_SENSORS_GPIO_FAN=m and CONFIG_SENSORS_PWM_FAN=m;
- *	- kernel rebuid;
- *	- DC Fan connected to GPIO via a N-MOSFET (2N7002)
+ *	- kernel configurations: CONFIG_SENSORS_GPIO_FAN=m;
+ *	- kernel rebuild;
+ *	- N-MOSFET connected to gpiopin, 2N7002-[https://en.wikipedia.org/wiki/2N7000];
+ *	- DC Fan connected to N-MOSFET Drain terminal, a 12V fan is working fine and quite silently;
+ *	  [https://www.tme.eu/en/details/ee40101s1-999-a/dc12v-fans/sunon/ee40101s1-1000u-999/]
  *
  *                   ┌─────────────────────┐
  *                   │Fan negative terminal│
  *                   └┬────────────────────┘
- *                    │
- *                 │──┘
+ *                    │D
+ *             G   │──┘
  * [GPIO12]──────┤ │<─┐  2N7002
  *                 │──┤
- *                    │
+ *                    │S
  *                   ─┴─
  *                   GND
  *
- * sudo dtc -W no-unit_address_vs_reg -@ -I dts -O dtb -o /boot/overlays/gpio-fan.dtbo gpio-fan.dts
- * sudo nano /boot/config.txt add "dtoverlay=gpio-fan" or "dtoverlay=gpio-fan,gpiopin=12,temp=45000"
- * or
- * sudo sh -c "echo '\n# Enable PI GPIO-Fan\ndtoverlay=gpio-fan\n' >> /boot/config.txt"
- * sudo sh -c "echo '\n# Enable PI GPIO-Fan\ndtoverlay=gpio-fan,gpiopin=12\n' >> /boot/config.txt"
+ * Build:
+ * 	- `sudo dtc -W no-unit_address_vs_reg -@ -I dts -O dtb -o /boot/overlays/gpio-fan.dtbo gpio-fan-overlay.dts`
+ * Activate:
+ *	- sudo nano /boot/config.txt add "dtoverlay=gpio-fan" or "dtoverlay=gpio-fan,gpiopin=12,temp=45000"
+ *	 or
+ *	- sudo sh -c 'printf "\n# Enable PI GPIO-Fan Default\ndtoverlay=gpio-fan\n" >> /boot/config.txt'
+ *	- sudo sh -c 'printf "\n# Enable PI GPIO-Fan Custom\ntoverlay=gpio-fan,gpiopin=12,temp=45000\n" >> /boot/config.txt'
  *
  */
 /dts-v1/;
@@ -52,7 +60,7 @@
 			trips {
 				cpu_hot: trip-point@0 {
 					temperature = <55000>;	/* (millicelsius) Fan started at 55°C */
-					hysteresis = <5000>;	/* (millicelsius) Fan stopped at 50°C */
+					hysteresis = <10000>;	/* (millicelsius) Fan stopped at 45°C */
 					type = "active";
 				};
 			};