Libgpiod Support

[fschrempf]

The GPIO sysfs interface in the Linux Kernel has been deprecated since 2015 and has been scheduled for removal. Nowadays it still exists in the kernel, but distros are starting to disable it. As already mentioned in #1569 (comment) recent versions of Debian Bookworm (and the new Debian 13 "Trixie") don't have the GPIO sysfs interface anymore.

If I understand this correctly, this means that labgrid is effectively not compatible with these distros anymore and hardware like the Raspberry Pi can't be used with their latest OS version.

I've read through #468 and I see that libgpiod support is not an easy task, but I guess there is no way to avoid solving this problem in some way.

[jluebbe]

The gpiod design is not compatible with that we need for labgrid: keeping the output active even if the process terminates. In the meantime the GPIO maintainers have agreed that the gpiod API is not working for all existing users, so they've build and merged (for v6.17) a new sysfs API which solves global GPIO numbering problem:
https://lore.kernel.org/all/20250704-gpio-sysfs-chip-export-v4-0-9289d8758243@linaro.org/

It seems, that the SYSFS API was removed locally by Raspbian only. All Debian kernels still support this:
https://salsa.debian.org/search?search=GPIO_SYSFS&nav_source=navbar&project_id=18670&group_id=2107&search_code=true&repository_ref=debian%2Flatest

So I might argue this is an issue of Raspbian breaking the kernel's UAPI guarantee, although a proper replacement for the existing SYSFS API users was already being worked on upstream. ;)

[fschrempf]

Thanks @jluebbe! That's very valuable information. I wasn't aware of the new sysfs approach.

And yes, your argument of Raspi OS introducing a breaking change (even with a minor release) is something that I can relate to. I had a closer look at the Raspi kernel repo and it looks like the defconfigs for 6.6 and 6.12 all currently have CONFIG_GPIO_SYSFS=y. So this might have been a temporary regression that has already been fixed.