VAR-SOM-MX6 GPIO

VAR-SOM-MX6 - GPIO

GPIO state

The current state of the systems' GPIOs can be obtained in user-mode, as shown in the following example:

$ cat /sys/kernel/debug/gpio

The above command on Variscite's VAR-DVK-MX6 will show the following:

root@var-som-mx6:~# cat /sys/kernel/debug/gpio 
GPIOs 0-31, platform/209c000.gpio, 209c000.gpio:
 gpio-25  (phy-reset:           ) out lo  
GPIOs 32-63, platform/20a0000.gpio, 20a0000.gpio:
GPIOs 64-95, platform/20a4000.gpio, 20a4000.gpio:
 gpio-77  (ov5640_mipi_pwdn    ) out lo    
GPIOs 96-127, platform/20a8000.gpio, 20a8000.gpio:
 gpio-101 (tlv320aic3x reset   ) out lo    
 gpio-106 (ov5640_mipi_reset   ) out lo    
 gpio-110 (2194000.usdhc cd    ) in  lo    
 gpio-111 (2194000.usdhc ro    ) in  lo    
 gpio-120 (spi_imx             ) out lo    
 gpio-121 (ads7846_pendown     ) in  hi    
GPIOs 128-159, platform/20ac000.gpio, 20ac000.gpio:
 gpio-141 (PCIe reset          ) out lo    
GPIOs 160-191, platform/20b0000.gpio, 20b0000.gpio:
 gpio-178 (sysfs               ) out lo    
GPIOs 192-223, platform/20b4000.gpio, 20b4000.gpio:
 gpio-200 (wlan-en-regulator   ) out lo  

Each GPIO is defined as in or out and the state is shown as lo or hi.
For example pin 110 is the SD-Card card-detect.

When  SD-Card is removed the state will be:
gpio-110 (2194000.usdhc cd    ) in  hi 
When the SD-Card is plugged the state will be:
gpio-110 (2194000.usdhc cd    ) in  lo

Manipulating a single GPIO via /sys/class/gpio

GPIOs in i.MX6 are grouped in groups of 32 pins.
For example GPIO1_3 belong to the first group pin 3. Its absolute number will be 3.
GPIO7_4 will be (7-1)*32+4=196.
Lets assume that you defined this GPIO in the device tree. We will show in the following sections how to define it.
To configure as output:

$ echo 196 > /sys/class/gpio/export
$ echo out > /sys/class/gpio/gpio196/direction

Set GPIO high:
$ echo 1 > /sys/class/gpio/gpio196/value
Set GPIO low:
$ echo 0 > /sys/class/gpio/gpio196/value

To configure as input:

$ echo 196 > /sys/class/gpio/export
$ echo in > /sys/class/gpio/gpio196/direction

$ cat /sys/class/gpio/gpio196/value
Will read the current value.

Kernel Device Tree GPIO configuration

Device Tree GPIO files

Pin Func files

In the Linux kernel in directory arch/arm/boot/dts/ you will find the pin functions files.
The relevant files are: imx6dl-pinfunc.h, imx6ul-pinfunc.h, imx6q-pinfunc.h depend on the platform we are running. If you edit imx6q-pinfunc.h and search for GPIO7_IO04 for example you will see a group of pins with same prefix "MX6QDL_PAD_SD3_DAT0".
#define MX6QDL_PAD_SD3_DAT0__SD3_DATA0 0x2c0 0x6a8 0x000 0x0 0x0
#define MX6QDL_PAD_SD3_DAT0__UART1_CTS_B 0x2c0 0x6a8 0x000 0x1 0x0
#define MX6QDL_PAD_SD3_DAT0__UART1_RTS_B 0x2c0 0x6a8 0x91c 0x1 0x2
#define MX6QDL_PAD_SD3_DAT0__FLEXCAN2_TX 0x2c0 0x6a8 0x000 0x2 0x0
#define MX6QDL_PAD_SD3_DAT0__GPIO7_IO04 0x2c0 0x6a8 0x000 0x5 0x0
Selecting one of them and writing it in the dts file will set the functionality required for this pin.

Variscite dts files

Variscite defines dts file for each platform.

Device Tree Name	Include dtsi file	SOM type	Carrier Board type	LCD Type	Evaluation Kit name
imx6q-var-som.dts	imx6qdl-var-som.dtsi	VAR-SOM-MX6_V2 (Quad / Dual)	VAR-MX6CustomBoard	Capacitive/Resistive touch	VAR-DVK-MX6_V2-PRO VAR-STK-MX6_V2
imx6q-var-som-vsc.dts	imx6qdl-var-som.dtsi	VAR-SOM-MX6_V2 (Quad / Dual)	VAR-SOLOCustomBoard	Capacitive LVDS touch	N/A
imx6dl-var-som.dts	imx6qdl-var-som.dtsi	VAR-SOM-MX6_V2 (DualLite/ Solo)	VAR-MX6CustomBoard	Capacitive/Resistive touch	N/A
imx6dl-var-som-solo-vsc.dts	imx6qdl-var-som.dtsi	VAR-SOM-SOLO / VAR-SOM-DUAL	VAR-SOLOCustomBoard	Capacitive LVDS touch	VAR-DVK-SOLO/DUAL VAR-STK-SOLO/DUAL
imx6dl-var-som-solo.dts	imx6qdl-var-som.dtsi	VAR-SOM-SOLO / VAR-SOM-DUAL	VAR-MX6CustomBoard	Capacitive/Resistive touch	N/A
imx6q-var-dart.dts	imx6qdl-var-dart.dtsi	VAR-SOM-SOLO / VAR-SOM-DUAL	VAR-DT6CustomBoard	Capacitive LVDS touch	VAR-STK-DT6.VAR-DVK-DT6

imx6q-var-som.dts starts with definitions and includindg dtsi files.
#define VAR_SOM_MX6

#include "imx6q.dtsi"
#include "imx6qdl-var-som.dtsi"
The imx6q.dtsi define the CPU platform and which pinfunc file will be included. This feature allow the pin name to be agnostic to the CPU type (i.MX6Q vs i.MX6DL)
imx6qdl-var-som.dtsi has the major VAR-SOM-MX6 definitions.

Define a pin as GPIO in the kernel Device Tree

First you need to modify the relevant device tree and make sure your gpio is defined.
For Example:
Edit arch/arm/boot/dts/imx6qdl-var-som.dtsi and in the section below:
hog {
pinctrl_hog_1: hoggrp-1 {
fsl,pins = <
/* CTW6120 IRQ */
MX6QDL_PAD_EIM_DA7__GPIO3_IO07 0x80000000
/* Touch */
/* for Bluetooth/wifi enable */
/* SDMMC2 CD/WP */
MX6QDL_PAD_KEY_COL4__GPIO4_IO14 0x80000000
MX6QDL_PAD_KEY_ROW4__GPIO4_IO15 0x80000000
/* USBOTG ID pin */
/* PMIC INT */
MX6QDL_PAD_GPIO_17__GPIO7_IO12 0x80000000
/* Wifi Slow Clock */
MX6QDL_PAD_ENET_RXD0__OSC32K_32K_OUT 0x000b0 /* WIFI Slow clock */
/* Audio Clock */
MX6QDL_PAD_GPIO_0__CCM_CLKO1 0x130b0 /* Audio Codec Clock */
/* Camera Clock */
MX6QDL_PAD_GPIO_3__CCM_CLKO2 0x130b0 /* Camera MCLK */
>;
};
Add the relevant GPIO to the above section in the device tree.

Device Tree GPIO attribute

If you look at Documentation/devicetree/bindings/pinctrl/fsl,imx6q-pinctrl.txt the number to the right of the pin control spec can be used for additional attributes like pull-ups, pull-downs, keepers, drive strength, etc.
The value 0x80000000 is don't know value please use the default". Else use the table below to set it to the required value.

CONFIG bits definition	value
PAD_CTL_HYS	(1 << 16)
PAD_CTL_PUS_100K_DOWN	(0 << 14)
PAD_CTL_PUS_47K_UP	(1 << 14)
PAD_CTL_PUS_100K_UP	(2 << 14)
PAD_CTL_PUS_22K_UP	(3 << 14)
PAD_CTL_PUE	(1 << 13)
PAD_CTL_PKE	(1 << 12)
PAD_CTL_ODE	(1 << 11)
PAD_CTL_SPEED_LOW	(1 << 6)
PAD_CTL_SPEED_MED	(2 << 6)
PAD_CTL_SPEED_HIGH	(3 << 6)
PAD_CTL_DSE_DISABLE	(0 << 3)
PAD_CTL_DSE_240ohm	(1 << 3)
PAD_CTL_DSE_120ohm	(2 << 3)
PAD_CTL_DSE_80ohm	(3 << 3)
PAD_CTL_DSE_60ohm	(4 << 3)
PAD_CTL_DSE_48ohm	(5 << 3)
PAD_CTL_DSE_40ohm	(6 << 3)
PAD_CTL_DSE_34ohm	(7 << 3)
PAD_CTL_SRE_FAST	(1 << 0)
PAD_CTL_SRE_SLOW	(0 << 0)