gps-share: specify /dev path to GPS device

hosts/common/programs/gps-share.nix

@@ -10,12 +10,29 @@
 # 3. provide a *read-only* API to clients like Geoclue.
 #    that is, expose the GPS device *output* to a client, but don't let the client write to the device (e.g. enable/disable the GPS).
 #    this is the primary function i derive from gps-share
-{ ... }:
+{ config, lib, ... }:
+let
+  cfg = config.sane.programs.gps-share;
+in
 {
   sane.programs.gps-share = {
-    services.gps-share = {
+    configOption = with lib; mkOption {
+      default = {};
+      type = types.submodule {
+        options.device = mkOption {
+          type = types.nullOr types.str;
+          default = null;
+          description = ''
+            path to GPS device to share.
+          '';
+          example = "/dev/ttyUSB1";
+        };
+      };
+    };
+
+    services.gps-share = lib.mkIf (cfg.config.device != null) {
       description = "gps-share: make local GPS serial readings available over Avahi";
-      command = "gps-share";  #< TODO: do i need to run it with any args?
+      command = "gps-share ${cfg.config.device}";
       dependencyOf = [ "geoclue-agent" ];
     };
   };

hosts/modules/hal/pine64.nix

@@ -283,6 +283,9 @@ in
       dd if=${pkgs.tow-boot-pinephone}/Tow-Boot.noenv.bin of=$out bs=1024 seek=8 conv=notrunc
     '';
 
+    sane.programs.gps-share.config = {
+      device = "/dev/ttyUSB1";
+    };
     sane.programs.swaynotificationcenter.config = {
       backlight = "backlight";  # /sys/class/backlight/*backlight*/brightness
     };