DESK-MX8M-L/Peripherals/GPIOs

History
Issue Date	Notes
2022/01/14	First DESK-MX8M-L release
2023/02/24	DESK-MX8M-L-2.0.0 release
2023/08/22	DESK-MX8M-L-4.0.0 release

Peripheral GPIOs

i.MX8 can handle external pins in many different ways and most of them can be configured as GPIOs. When a pin is set as a GPIO, it is possible to read its value, change its direction or change output value directly from the shell.

Device tree configuration

ORCA SOM

Here below a simple example of device tree configuration for using a GPIO on DAVE's kit for the ORCA SOM with gpio-leds sysfs interface:

From imx8mp-mito8mplus-cb1001.dts:

	leds {
		compatible = "gpio-leds";

		ptn36043_gpio {
			/* this gpio set the USB-C crossbar switch direction.
			 * As the connected peripheral would always be the power source of
			 * the system, hotplug is not possible.
			 * It's status is configured by the bootloader according to the CC
			 * direction and has only to be preserved during the execution.
			 * see usb_dwc3_0 for more details */
			gpios = <&gpio1 12 GPIO_ACTIVE_HIGH>;
			default-state = "keep";
		};
	};
...
...
&iomuxc {
...
...
	pinctrl_gpio_led: gpioledgrp {
		fsl,pins = <
			MX8MP_IOMUXC_NAND_READY_B__GPIO3_IO16	0x19
		>;
	};
...
...
};

Accessing the peripheral in ORCA SOM

Linux messages at boot time

With the previous leds configuration for the GPIOs, it is possible to find them on sysfs under /sys/class/leds sub-directory:

root@desk-mx8mp:~# ls -la /sys/class/leds/
total 0
drwxr-xr-x  2 root root 0 Jul 26 05:52 .
drwxr-xr-x 87 root root 0 Jul 26 05:52 ..
lrwxrwxrwx  1 root root 0 Jul 26 05:52 mmc0:: -> ../../devices/platform/soc@0/30800000.bus/30b40000.mmc/leds/mmc0::
lrwxrwxrwx  1 root root 0 Jul 26 05:52 mmc1:: -> ../../devices/platform/soc@0/30800000.bus/30b50000.mmc/leds/mmc1::
lrwxrwxrwx  1 root root 0 Jul 26 05:52 mmc2:: -> ../../devices/platform/soc@0/30800000.bus/30b60000.mmc/leds/mmc2::
lrwxrwxrwx  1 root root 0 Jul 26 05:52 ptn36043_gpio -> ../../devices/platform/leds/leds/ptn36043_gpio
root@desk-mx8mp:~#

Usage as led function

Setting the brightness node, it is possible to change the GPIO status:

• read actual led/GPIO status

root@desk-mx8mp:~# cat /sys/class/leds/ptn36043_gpio/brightness 
1
root@desk-mx8mp:~#

• change led/GPIO status to Low (0)

root@desk-mx8mp:~# echo 0 > /sys/class/leds/ptn36043_gpio/brightness                                                                                                                                                                          
root@desk-mx8mp:~# [ 7970.890896] usb 2-1: USB disconnect, device number 2

• change led/GPIO status to High (1)

root@desk-mx8mp:~# echo 1 > /sys/class/leds/ptn36043_gpio/brightness                                                                                                                                                                          
root@desk-mx8mp:~# [ 7978.902356] usb 2-1: new SuperSpeed USB device number 5 using xhci-hcd
[ 7979.060143] hub 2-1:1.0: USB hub found
[ 7979.064524] hub 2-1:1.0: 4 ports detected
root@desk-mx8mp:~#

Usage with sysfs

It is possible to configure the GPIO pin directly at Linux userspace using sysfs even if it is discouraged: see below .

See here below, an example of configuring a GPIO pin using J8 connector:

• set J8.11 SAI2_RXD0 (MX8MP_IOMUXC_SAI2_RXD0__GPIO4_IO23) as output GPIO
  • GPIO4_IO23 => (n-1)*32 + IO = (4-1)*32+23 = 119

• export the GPIO

root@desk-mx8mp:~# echo 119 > /sys/class/gpio/export

Using the GPIO as output

root@desk-mx8mp:~# echo out > /sys/class/gpio/gpio119/direction

• set the GPIO level

root@desk-mx8mp:~# echo 1 > /sys/class/gpio/gpio119/value
root@desk-mx8mp:~# cat /sys/class/gpio/gpio119/value                                                                                                                                                                                          
1
root@desk-mx8mp:~# echo 0 > /sys/class/gpio/gpio119/value                                                                                                                                                                                     
root@desk-mx8mp:~# cat /sys/class/gpio/gpio119/value 
0
root@desk-mx8mp:~#

For using the GPIO as input:

root@desk-mx8mp:~# echo in > /sys/class/gpio/gpio119/direction

• read the GPIO level

root@desk-mx8mp:~# cat /sys/class/gpio/gpio119/value
0
root@desk-mx8mp:~#

Note that on i.MX SoC the GPIO value can be read back only if the SION bit is set the pin muxing.

Additional information

Information about GPIOs usage under sysfs directory https://www.kernel.org/doc/Documentation/gpio/sysfs.txt

GPIO sysfs deprecated

sysfs GPIO ABI has been deprecated. See more information here about it. A character device access has to be used, more information here

Information about GPIOs library libgpiod - C library and tools - can be found on git.kernel.org

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