raspberry-pi/4/i2c1: factor out easy dts into helper, add i2c0

raspberry-pi/4/default.nix

@@ -4,6 +4,7 @@
   imports = [
     ./audio.nix
     ./dwc2.nix
+    ./i2c0.nix
     ./i2c1.nix
     ./modesetting.nix
     ./poe-hat.nix

raspberry-pi/4/i2c0.nix

@@ -0,0 +1,25 @@
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.hardware.raspberry-pi."4".i2c0;
+  inherit (import ./overlay.nix) simple-pi4-overlay;
+in
+{
+  options.hardware = {
+    raspberry-pi."4".i2c0 = {
+      enable = lib.mkEnableOption ''
+        Turn on the VideoCore I2C bus (maps to /dev/i2c-22) and enable access from the i2c group.
+        After a reboot, i2c-tools (e.g. i2cdetect -F 22) should work for root or any user in i2c.
+       '';
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    hardware = {
+      i2c.enable = lib.mkDefault true;
+      deviceTree = {
+        overlays = [ (simple-pi4-overlay { target = "i2c0if"; status = "okay"; }) ];
+      };
+    };
+  };
+}

raspberry-pi/4/i2c1.nix

@@ -2,6 +2,7 @@
 
 let
   cfg = config.hardware.raspberry-pi."4".i2c1;
+  inherit (import ./overlay.nix) simple-pi4-overlay;
 in
 {
   options.hardware = {
@@ -15,29 +16,9 @@ in
 
   config = lib.mkIf cfg.enable {
     hardware = {
-      i2c.enable = true;
+      i2c.enable = lib.mkDefault true;
       deviceTree = {
-        overlays = [
-          # Equivalent to dtparam=i2c1=on
-          {
-            name = "i2c1-on-overlay";
-            dtsText = ''
-              /dts-v1/;
-              /plugin/;
-              / {
-                compatible = "brcm,bcm2711";
-                fragment@0 {
-                  target = <&i2c1>;
-                  __overlay__ {
-                    #address-cells = <1>;
-                    #size-cells = <0>;
-                    status = "okay";
-                  };
-                };
-              };
-            '';
-          }
-        ];
+        overlays = [ (simple-pi4-overlay { target = "i2c1"; status = "okay"; }) ];
       };
     };
   };

raspberry-pi/4/overlay.nix

@@ -0,0 +1,18 @@
+{
+  simple-pi4-overlay = { target, status }: {
+    name = "${target}-${status}-overlay";
+    dtsText = ''
+      /dts-v1/;
+      /plugin/;
+      / {
+        compatible = "brcm,bcm2711";
+        fragment@0 {
+          target = <&${target}>;
+          __overlay__ {
+            status = "${status}";
+          };
+        };
+      };
+    '';
+  };
+}