[RFC] GPIO support

[vbatts]

Current situation

As Flatcar is being included in more edge deployments (amd64 and arm64), there are integrations with devices needed (sensors, cameras, etc.), which is not included

Impact
blocks certain edge use-cases

Ideal future situation
GPIO is present so folks can continue doing cool stuff on Flatcar

Implementation options
CONFIG_GPIO_SYSFS so that /sys/class/gpio/... is present, and /dev/gpiomem is present

cc @janakiramm

[raballew]

@vbatts I am currently working on a custom build of Flatcar for Raspberry Pi 4B's so that I can deploy a sensor k8s cluster and would love help implementing this. But since I am quite new to Flatcar, could you point me in the right direction or is it just setting CONFIG_GPIO_SYSFS=y?

[t-lo]

I believe enabling CONFIG_GPIO_SYSFS is a good next step here.

Instructions for adding the kernel config are in the OS image build doc's kernel modules section. To get this change into Flatcar we need a PR to https://github.com/kinvolk/coreos-overlay/blob/main/sys-kernel/coreos-modules/files/commonconfig-5.10.

[jepio]

These options are present in current stable flatcar images.