How to initial GPIO as input or output PINS

tzeng015 — Wed, 30 Nov 2022 06:14:37 GMT

Platform : imx8mm

Linux : 5.10

I want to check the GPIO4_14 status . Here is my check list

u-boot

kernel

I can't see the GPIO4_14 status.

Anyone can help me to initial the GPIO input or output in which file ? I don't know where is the file can initial GPIO ?

Please help me.

thank you

tzeng015

Re: How to initial GPIO as input or output PINS

edwardtyrrell — Wed, 30 Nov 2022 12:22:11 GMT

Hi @tzeng015

See what you get with cat /sys/kernel/debug/gpio, sys/class/gpio is being deprecated and with new builds (i.e. mine) it's not even available.

For example my board gives:

cat /sys/kernel/debug/gpio
gpiochip0: GPIOs 0-31, parent: platform/30200000.gpio, 30200000.gpio:
gpio-15 ( |cd ) in hi IRQ ACTIVE LOW

gpiochip1: GPIOs 32-63, parent: platform/30210000.gpio, 30210000.gpio:
gpio-42 ( |reset ) out hi ACTIVE LOW
gpio-51 ( |regulator-usdhc2 ) out lo

Also, unlike /sys/class/gpio, pins used with gpiod need to be in your device-tree pinctrl_hog to work.

opinctrl_hog: hoggrp {
fsl,pins = <
MX8MM_IOMUXC_SAI5_RXD0_GPIO3_IO21 0x19
MX8MM_IOMUXC_SAI5_RXD1_GPIO3_IO22 0x19
MX8MM_IOMUXC_SAI5_RXD2_GPIO3_IO23 0x19
MX8MM_IOMUXC_SAI5_RXD3_GPIO3_IO24 0x19
>;
};

One other thing, be careful with gpioset as the gpiod's start at gpiochip0 where the iMX8 mux registers start at 1. Whether 'gpio state -a' in UBoot is offset by one I haven't tried. Here's an example of using gpiod in userspace:

Pin MX8MM_IOMUXC_SAI5_RXD0_GPIO3_IO21

Set GPIO3_21 high: // As above
gpioset gpiochip2 21=1

Set GPIO3_21 low: // As above
gpioset gpiochip2 21=0

Check the line with a scope or the memory read command /unit_tests/memtool -32 <Address> 1

3022_0000 GPIO data register (GPIO3_DR) // Page 1691 of Ref manual

/unit_tests/memtool -32 0x30220000 1
E
Reading 0x1 count starting at address 0x30220000

0x30220000: 00200000 // if GPIO3_21 is high,

0x30220000: 00000000 // If low

Hope this helps.

topic How to initial GPIO as input or output PINS in i.MX Processors

How to initial GPIO as input or output PINS

Re: How to initial GPIO as input or output PINS