Nixpkgs: Raspberry Pi 3 B+ wifi does not work until the service is restarted

[ertw]

Describe the bug
I would like to have my Rasberry Pi connect to wifi without requiring user interaction. I have attempted to configure it using both wpa_supplicant and iwd, and both services are in a failed state on initial login. I have tried wpa_supplicant both with & without connman, and with & without declaratively specifying the connection details of the SSID.

Restarting the service (systemctl restart wpa_supplicant.service or systemctl restart iwd.service) causes the wireless to immediately connect, and systemctl status shows the service in a healthy state.

When I run journalctl -u iwd, I see the following error listed:
NEW_INTERFACE failed: Device or resource busy

To Reproduce
Steps to reproduce the behavior:

1. Install NixOs 19.09 with kernel 4.19 following the wiki guide
2. Attempt to configure wifi using network.wireless.enable = true; or network.wireless.iwd.enable = true;

Expected behavior
The pi should connect to wifi, and the wireless service (iwd or wpa_supplicant) should not crash.

Metadata
Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

 - system: `"aarch64-linux"`
 - host os: `Linux 4.19.107, NixOS, 19.09.2201.7d31bbceaa1 (Loris)`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.3.3`
 - channels(root): `"nixos-unstable-20.09pre215947.82b54d49066, nixos-19.09.2201.7d31bbceaa1"`
 - channels(ertw): `"nixpkgs-unstable-20.09pre215991.93ba4ecd586"`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute:
# a list of nixos modules affected by the problem
module:

[matthewbauer]

I had to add this to my config for wifi to work:

  boot.extraModprobeConfig = ''
    options cfg80211 ieee80211_regdom="${regDom}"
  '';
  hardware.firmware = [ pkgs.wireless-regdb ];

where regDom is your 2 letter country code (US for the United States).

[ertw]

Update: I did try @matthewbauer's suggestion, and I'm not sure whether it helped or not. Now I am sometimes getting connected to wifi, and sometimes not. In the case where it fails to connect to wifi, I see the same NEW_INTERFACE failed: Device or resource busy in systemctl status.

I am also still unable to boot into the latest 5.4 kernel (I reported a separate bug for this), so maybe this is an issue that is been fixed, and is only affecting 4.19?

Is there some way I can configure the systemd unit to always restart? Something like, attempt to start every 5 seconds forever seems like what I'd want regardless in an embedded device where connectivity is critical.

[matthewbauer]

I think you can do:

systemd.services.iwd.serviceConfig.Restart = "always";

I also have this in my settings, but can't remember if it made a difference:

networking.dhcpcd.extraConfig = "timeout 0";

[ertw]

Okay, systemd.services.iwd.serviceConfig.Restart = "always"; does seem to solve my problem- the device is now connecting reliably to wifi and I can SSH into it without needing a display.

I'd like to leave this issue open for now though, as there is something causing both iwd and wpa_supplicant to crash on initial startup. Ideally we could discover what this is, and correctly solve for it rather than just restarting the service.

Here is what I believe to be the minimal config for working WLAN on the Raspberry Pi 3 B+:

{ config, pkgs, lib, ... }:
{
  systemd.services.iwd.serviceConfig.Restart = "always";
  hardware = {
    enableRedistributableFirmware = true;
    firmware = [ pkgs.wireless-regdb ];
  };
  networking = {
    useDHCP = false;
    interfaces.wlan0.useDHCP = true;
    networkmanager.wifi.backend = "iwd";
    wireless.iwd.enable = true;
  };
  boot = {
    extraModprobeConfig = ''
      options cf680211 ieee80211_regdom="US"
    '';
  };
  system = {
    stateVersion = "19.09";
  };
}

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/raspberry-pi-aarch64-connect-to-wifi-automatically/6162/2

[ertw]

To add to this, the Arch Linux iwd entry specifically calls out issues with the systemd unit failing on startup, which sounds like what I've been running into.

https://wiki.archlinux.org/index.php/Iwd#Systemd_unit_fails_on_startup_due_to_device_not_being_available

[mleonhard]

My Raspberry Pi 4B was failing to load the wlan0 device. The fix is to add hardware.enableRedistributableFirmware = true;. The full working config is in https://github.com/Robertof/nixos-docker-sd-image-builder/issues/10#issuecomment-646901392

Shall we close this issue?