From 1f5b1539e423410d70975118754e5dfe25b97b15 Mon Sep 17 00:00:00 2001
From: Aditya Prayoga <aditya@kobol.io>
Date: Tue, 27 Oct 2020 18:07:35 +0700
Subject: [PATCH] Helios64: Update GPIO usage and SATA

---
 docs/helios64/gpio.md | 80 +++++++++++++++++++++++++++++++++++++++++++
 docs/helios64/sata.md |  2 ++
 2 files changed, 82 insertions(+)

diff --git a/docs/helios64/gpio.md b/docs/helios64/gpio.md
index 37516d9..3e6632f 100644
--- a/docs/helios64/gpio.md
+++ b/docs/helios64/gpio.md
@@ -28,3 +28,83 @@ Helios64 provides 16 GPIOs via a 20-Pin header (P5). Those GPIOs are provided vi
 | 18  | EXP_P1_6 | |
 | 19  | EXP_P1_7 | |
 | 20  | - | GND |
+
+## Accessing GPIOs under Linux
+
+If the kernel supports debugfs (*CONFIG_DEBUG_FS=y*), list of GPIOs can be retrieved with the following command
+
+```bash
+sudo cat /sys/kernel/debug/gpio
+```
+
+Look for the **gpiochip5: GPIOs XXX-YYY** section, whereas **XXX** is first GPIO number and **YYY** is last GPIO number of IO expander.
+
+```
+gpiochip5: GPIOs 496-511, parent: i2c/2-0020, 2-0020, can sleep:   
+```
+
+Another way to get first GPIO number of the IO expander
+
+```
+cat /sys/bus/i2c/devices/2-0020/gpio/gpiochip*/base
+```
+
+Therefore the mapping between header P5 Pins and Sysfs GPIO numbers will be as described in the following table
+
+### GPIO Table
+
+| PIN | Sysfs GPIO number | Remarks |
+|-----|------|-------------|
+| 1   | - | 3.3V Supply |
+| 2   | - | 5V Supply |
+| 3   | - | GND |
+| 4   | 496 | |
+| 5   | 497 | |
+| 6   | 498 | |
+| 7   | 499 | |
+| 8   | 500 | |
+| 9   | 501 | |
+| 10  | 502 | |
+| 11  | 503 | |
+| 12  | 504 | |
+| 13  | 505 | |
+| 14  | 506 | |
+| 15  | 507 | |
+| 16  | 508 | |
+| 17  | 509 | |
+| 18  | 510 | |
+| 19  | 511 | |
+| 20  | - | GND |
+
+### GPIO Control
+
+**1.** Export the GPIO number you want to use
+
+```
+echo N | sudo tee -a /sys/class/gpio/export
+```
+
+**2.** Set the direction, "out" for Output or "in" for Input
+
+```
+echo DIRECTION | sudo tee -a /sys/class/gpio/gpioN/direction
+```
+
+**3.** Now you can read or change the GPIO value
+
+To read GPIO value
+
+```
+cat /sys/class/gpio/gpioN/value
+```
+
+To change GPIO value (only if GPIO set as Output)
+
+```
+echo VALUE | sudo tee -a /sys/class/gpio/gpioN/value
+```
+
+!!! notes
+    Pay attention to the path, /sys/class/gpio/gpio**N**/ where **N** is the GPIO number.
+
+
diff --git a/docs/helios64/sata.md b/docs/helios64/sata.md
index 3782f1f..6c6a865 100644
--- a/docs/helios64/sata.md
+++ b/docs/helios64/sata.md
@@ -37,6 +37,8 @@ The power delivery of the HDDs is devided into two group:
 
 Helios64 implements a power staggering approach where *HDD Rail A* will be powered up first, then few seconds later *HDD Rail B* will be powered up. This power control scenario is performed to reduce the inrush current during disk spin-up.
 
+The power staggering mechanism is not user configurable. It is done by bootloader.
+
 ### J8 Pinout
 
 ![J8 Location](/helios64/img/sata/j8_pinout.jpg)