GPIO in kernel mode

Technical Support
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1

I want to experiment with accessing Apalis GPIO pins from a kernel driver. To that end, I’m trying to use gpio_request_array() to request the gpio pins when I load the module. The call fails. The pins I want to access come pre-exported and I can’t seem to unexport any of them:

root@apalis-t30:~# cd /sys/class/gpio/
root@apalis-t30:/sys/class/gpio# ls
export       gpio147      gpio150      gpio220      gpio223      gpiochip0
gpio129      gpio148      gpio216      gpio221      gpio225      gpiochip256
gpio146      gpio149      gpio219      gpio222      gpio226      unexport
root@apalis-t30:/sys/class/gpio# echo 146 > unexport 
-sh: echo: write error: Invalid argument

So how do I get access to the pins in a kernel mode driver?

2

Those GPIOs are requested in linux kernel during platform initialisation. There is an array called apalis_t30_gpios in arch/arm/mach-tegra/board-apalis_t30.c that defines which GPIOs will be exported. Adjust it as required and rebuild the kernel.

3

And there it is, right in front of my eyes. Thanks, this is exactly what I’m looking for.

4

You are welcome. Thanks for the feedback.