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Raspberry Pi: gpiomem device support



Good Day!

I've tried to get GPIO access working on 1B (Raspberry Pi B+) images from [1], however, the "/dev/gpiomem" device is missing and access to "/dev/mem" (some libaries fall back to that device) is denied (even as root, and I don't even want to use "/dev/mem").

Searching the internet brough up some udev rules. So I tried thse without success:

SUBSYSTEM=="gpio", GROUP="gpio", MODE="0660"
KERNEL=="gpiomem", GROUP="gpio", MODE="0660"
SUBSYSTEM=="bcm2835-gpiomem", GROUP="gpio", MODE="0660"
SUBSYSTEM=="bcm2835-gpiomem", KERNEL=="gpiomem", GROUP="gpio", MODE="0660"

I later found /lib/udev/rules.d/60-rpi.gpio-common.rules and added these rules. Also no success.

I can't find "gpiomem" in the kernel config.

In the official Raspberry Pi repository there once was a request [2] to enable a kernel config "CONFIG_BCM2835_DEVGPIOMEM". This module was apparently replaced by something called "raspberrypi-gpiomem" in commit 27543eeff4553f5caf7c6d8763c566042b047af0. Interestingly I can't find that phrase in any other commit in their repo.

(Note: I'm aware that Debian does not refer to the Raspberry Pi [2] repo, this just came up in my research.)

To me there seems to be kernel support missing or a config is not set.

Can someone please clarify on this?


Thank you.

Best regards,
Thomas.


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