iio-sensor-proxy: implement partial magnetometer support

TODO.md

@@ -128,6 +128,7 @@
     - this is a problem of playerctld, i guess
   - add option to change audio output
 - moby: tune GPS
+  - fix iio-sensor-proxy magnetometer scaling
   - tune QGPS setting in eg25-control, for less jitter?
   - configure geoclue to do some smoothing?
   - manually do smoothing, as some layer between mepo and geoclue?

hosts/common/programs/iio-sensor-proxy.nix

@@ -15,21 +15,30 @@
 #
 # HARDWARE SUPPORT: PINEPHONE (2024/07/01)
 # - accelerometer and light sensor seem to work
-# - magnetometer IS NOT SUPPORTED
+# - magnetometer (af8133j, different but similar to lis3mdl) IS NOT SUPPORTED
 #   - <https://gitlab.freedesktop.org/hadess/iio-sensor-proxy/-/issues/310>
 #   - exists in sysfs and can be viewed with
 #     `cat /sys/devices/platform/soc/1c2b000.i2c/i2c-1/1-001c/iio:device2/in_magn_x_raw`
 #   - nothing in iio-sensor-proxy reads anything related to "magn".
-#   - my sensor is af8133j -- different but similar to lis3mdl listed in issue report,
-#   - seems i could add a new "polling" iio-sensor-proxy driver which reads the data from sysfs pretty easily.
-#     not sure how much post-processing needs to happen on that data, but i doubt it's too much?
-#   - TODO: try using this implementation that's out for PR: <https://gitlab.freedesktop.org/hadess/iio-sensor-proxy/-/merge_requests/316>
-{ config, lib, ... }:
+#   - WIP PR to support magnetometers: <https://gitlab.freedesktop.org/hadess/iio-sensor-proxy/-/merge_requests/316>
+#     - after rebase, it *functions*, but does not scale the readings correctly
+#       heading changes only over the range of 50 - 70 deg.
+{ config, lib, pkgs, ... }:
 let
   cfg = config.sane.programs.iio-sensor-proxy;
 in
 {
   sane.programs.iio-sensor-proxy = {
+    packageUnwrapped = pkgs.iio-sensor-proxy.overrideAttrs (upstream: {
+      patches = (upstream.patches or []) ++ [
+        (pkgs.fetchpatch {
+          name = "WIP:compass: Add support for polling uncalibrated devices";
+          # url = "https://gitlab.freedesktop.org/hadess/iio-sensor-proxy/-/merge_requests/316.diff";
+          url = "https://git.uninsane.org/colin/iio-sensor-proxy/commit/fd21f1f4bf1eadd603b1f24f628b979691d9cf3b.diff";
+          hash = "sha256-+GoEPby6q+uSkQlZWFWr5ghx3BKBMGk7uv/DDhGnxDk=";
+        })
+      ];
+    });
     enableFor.system = lib.mkIf (builtins.any (en: en) (builtins.attrValues cfg.enableFor.user)) true;  #< for dbus/polkit policies
   };
   services.udev.packages = lib.mkIf cfg.enabled [ cfg.package ];