Can't access GPIO on Debian Buster & Pi4B

Question

I'm running a Pi4 with Debian Buster (not Raspbian / RaspberryPi OS) and need to interact with the GPIO pins but am having problems doing so.

I've created a gpio group and added the pi user to it along with setting the file permissions and group accordingly (re:GPIO Permission Denied). However accessing GPIO18 and other gives me the following error:

> sudo sh -c 'echo 18 >/sys/class/gpio/export'
> sh: 1: echo: echo: I/O error

or

> echo 18 >/sys/class/gpio/export
> -bash: echo: write error: Invalid argument

If I run ls /sys/class/gpio I get:

> export gpiochip446  gpiochip454  unexport

I can see (cant recall the command used) the gpiochip454 handles 58 pins and is the Broadcom BCM2711 which handles the GPIO. As a test I tried to export various GPIO pin numbers but none of them worked if below the gpiochip number. However, all (58) numbers from the gpiochip number upwards, do export.

So, I took a guess and assumed that if I counted up 18 pings from the gpiochip number (gpio472), I should be able to interact with gpio18, but this did not shutdown the power management board that reacts to gpio18. I also tried using the physical pin number(12) and adding this to the chip number giving me gpio466. Again, this did nothing, although in both cases I do see these pins being exported and visible via ls /sys/class/gpio.

> ls -l /dev/gpiochip*
 crw------- 1 root root 254, 0 Jan  4 16:06 /dev/gpiochip0
 crw------- 1 root root 254, 1 Jan  4 16:06 /dev/gpiochip1

Is there a way that I can use the gpio number like I would on Raspbian / Raspberrypi OS ?

I'm now at a loss as to what I need to do to get this working and would appreciate some help in working this out.

Thanks.

Answer 1

I don't know why the sysfs exports aren't working. I tried a few variants of your commands but they did not work.

Given that the /dev/gpiochip devices exist you could use that interface instead.

I have a new /dev/gpiochip library suite called lg.

http://abyz.me.uk/lg/

You could use that to manipulate the GPIO.

I have added some details at https://elinux.org/C

Answer 2

I'm using a fresh aarch64 with Arch Linux on a RPi 4B, and had the same issue with echoing low numbers to /sys/class/gpio/export. Reading more, I see that the sysfs approach is legacy and probably being dropped from newer kernels. The character device ABI, using /dev/gpiochip[0-9]+ (as discussed by @joan), is the new way to access GPIOs.

On Arch, the gpio-utils package offers lsgpio, gpio-watch, gpio-hammer, gpio-event-mon as easy CLI tools for interacting with GPIO character devices. On Debian Buster, package gpiod provides gpioget, gpioinfo, gpiomon, gpioset, which may do the same.