DART-6UL GPIO

DART-6UL- GPIO

GPIO state

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

root@imx6ul-var-dart:~# cat /sys/kernel/debug/gpio
GPIOs 0-31, platform/209c000.gpio, 209c000.gpio:
 gpio-10  (phy-reset           ) out lo    

GPIOs 32-63, platform/20a0000.gpio, 20a0000.gpio:

GPIOs 64-95, platform/20a4000.gpio, 20a4000.gpio:
 gpio-68  (ft5x06_irq_gpio     ) in  hi    

GPIOs 96-127, platform/20a8000.gpio, 20a8000.gpio:
 gpio-115 (2190000.usdhc cd    ) in  hi    
 gpio-116 (IDE Activity        ) out lo    
 gpio-117 (Heart Beat          ) out lo    

GPIOs 128-159, platform/20ac000.gpio, 20ac000.gpio:
 gpio-128 (phy-reset           ) out lo 

Each GPIO is defined as in or out and the state is shown as lo or hi.
For example pin 115 is the SD card card-detect. When an SD card is plugged in, the state will be:

 gpio-115 (2190000.usdhc cd    ) in  lo

When the SD card is removed, the state will be:

 gpio-115 (2190000.usdhc cd    ) in  hi

Manipulating a single GPIO via /sys/class/gpio

GPIOs in i.MX 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.
Assuming this GPIO is defined in your device tree, the following is an example of how to use it from userspace.

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

Read the current value:

$ cat /sys/class/gpio/gpio196/value

Kernel Device Tree GPIO configuration

Device Tree GPIO files

Pin Func files

In the directory arch/arm/boot/dts/ of the Linux kernel source you will find the pin functions definitions files.
The relevant file is imx6ul-pinfunc.h.
If you edit it and search for GPIO4_IO24, for example, you will see a group of definitions with same prefix (pad name), "MX6UL_PAD_CSI_DATA03".

#define	MX6UL_PAD_CSI_DATA03__CSI_DATA05                         	0x01F0 0x047C 0x04CC 0 0
#define	MX6UL_PAD_CSI_DATA03__USDHC2_DATA3                       	0x01F0 0x047C 0x0688 1 0
#define	MX6UL_PAD_CSI_DATA03__SIM2_PORT1_PD                      	0x01F0 0x047C 0x0000 2 0
#define	MX6UL_PAD_CSI_DATA03__ECSPI2_MISO                        	0x01F0 0x047C 0x0548 3 0
#define	MX6UL_PAD_CSI_DATA03__EIM_AD03                           	0x01F0 0x047C 0x0000 4 0
#define	MX6UL_PAD_CSI_DATA03__GPIO4_IO24                         	0x01F0 0x047C 0x0000 5 0
#define	MX6UL_PAD_CSI_DATA03__SAI1_RX_BCLK                       	0x01F0 0x047C 0x0000 6 0
#define	MX6UL_PAD_CSI_DATA03__UART5_DCE_CTS                      	0x01F0 0x047C 0x0000 8 0
#define	MX6UL_PAD_CSI_DATA03__UART5_DTE_RTS                      	0x01F0 0x047C 0x0640 8 0

Adding only the one with the GPIO4_IO24 suffix (function) to your dts file will let you use the pin as GPIO.

Variscite dts files

Variscite defines dts file for each platform.

Device Tree Name	SOM type	Carrier Board type	LCD Type	Evaluation Kit name
imx6ul-var-dart.dts	DART-6UL	VAR-6ULCustomBoard	Capacitive/ touch	VAR-STK-6UL VAR-DVK-6UL

imx6ul-var-dart.dts starts with definitions and including dtsi files.

#include <dt-bindings/input/input.h>
#include "imx6ul.dtsi"

The imx6ul.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)
We create 4 DTB's out of imx6ul-var-dart.dts.

imx6ul-var-dart-nand_wifi.dts
imx6ul-var-dart-sd_nand.dts
imx6ul-var-dart-emmc_wifi.dt
imx6ul-var-dart-sd_emmc.dts 

They just define one of

/* #define WIFI */
/* #define EMMC */
/* #define  NAND  */

The WIFI and SCDARD share the same MMC interface. So only one of them can be activated at a time. The NAND and eMMC share the same interface I/O. So only one of them can be activated at a time.

Define a pin as GPIO in the kernel Device Tree

You need to add the relevant definitions to your device tree, as explained in the Pin Func files section above.
Edit arch/arm/boot/dts/arch/arm/boot/dts/imx6ul-var-dart.dts and add the definition for the GPIO you need in the section below.

	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_hog>;

	pinctrl-0 = <&pinctrl_hog_1>;
	imx6ul-evk {
		pinctrl_hog_1: hoggrp-1 {
			fsl,pins = <
				MX6UL_PAD_CSI_HSYNC__GPIO4_IO20		0x1b0b0 /* Led 1 */
				MX6UL_PAD_CSI_DATA00__GPIO4_IO21	0x1b0b0 /* Led 2 */
				MX6UL_PAD_GPIO1_IO00__GPIO1_IO00	0x17059	/* User Button */
				MX6UL_PAD_GPIO1_IO07__ENET2_MDC		0x1b0b0
				MX6UL_PAD_GPIO1_IO06__ENET2_MDIO	0x1b0b0
				MX6UL_PAD_SNVS_TAMPER4__GPIO5_IO04	0x1b0b0	/* BT Enable */
			>;
		};

Device Tree GPIO attribute

If you look at cat Documentation/devicetree/bindings/pinctrl/fsl,imx6ul-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)