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.
