dualsense: possibly fix weird vibrations

hosts/yarn/default.nix

@@ -16,6 +16,7 @@
     ./lact.nix
     ./vr.nix
     ./forza-trigger
+    ./dualsense-attenuation.nix
 
     inputs.impermanence.nixosModules.impermanence
   ];
@@ -173,4 +174,9 @@
 
   # PS5 DualSense adaptive triggers in Forza Horizon 4 / 5.
   services.forzaTrigger.enable = true;
+
+  # PS5 DualSense LRA whine fix: cap firmware-level haptic amplitude so the
+  # voice-coil actuators never hit their audible-buzz regime under heavy
+  # rumble. Independent of the forza-trigger adaptive trigger path.
+  services.dualsenseAttenuation.enable = true;
 }

hosts/yarn/dualsense-attenuation.nix

@@ -0,0 +1,93 @@
+# DualSense rumble/trigger firmware-level attenuation.
+#
+# The PS5 controller's haptic actuators are linear resonant actuators (LRAs) —
+# voice coils, not ERM rotors. When driven near max amplitude they emit an
+# audible high-pitched whine in addition to the intended rumble. This is a
+# hardware property of the actuator, not a kernel or Steam Input bug, and
+# can't be fixed in any rumble path that talks to the LRAs at full strength.
+#
+# Sony exposes a firmware knob ("rumble emulation amplitude modifier", in
+# DS_OUTPUT report 0x05/0x31, gated by valid_flag2 bit RUMBLE_EMULATION_SELECT)
+# that clamps haptic / trigger amplitude before the actuator is driven. This
+# module sends that report once on plug-in via dualsensectl. The setting
+# lives in controller RAM until the next power-cycle (USB unplug or BT
+# disconnect-with-power-off), so re-applying on every udev `add` covers
+# every reconnect.
+#
+# Coexists with Steam Input's rumble path: Steam writes rumble in the same
+# output report, but only sets COMPATIBLE_VIBRATION / HAPTICS_SELECT in
+# valid_flag0 — not RUMBLE_EMULATION_SELECT — so its writes don't reset the
+# attenuation. Verified live with Steam (gamepadui) and forza-trigger both
+# holding hidraw concurrently.
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+let
+  cfg = config.services.dualsenseAttenuation;
+
+  applyScript = pkgs.writeShellScript "dualsense-apply-attenuation" ''
+    set -eu
+    # Retry briefly: the hidraw node exists by udev `add`, but the device
+    # may still be settling its initial HID descriptor exchange. dualsensectl
+    # needs to read the firmware report before it can write attenuation.
+    for _ in 1 2 3 4 5 6 7 8 9 10; do
+      if ${pkgs.dualsensectl}/bin/dualsensectl -l 2>/dev/null | grep -q ":"; then
+        exec ${pkgs.dualsensectl}/bin/dualsensectl attenuation \
+          ${toString cfg.rumble} ${toString cfg.trigger}
+      fi
+      sleep 0.2
+    done
+    echo "no DualSense detected; nothing to attenuate" >&2
+    exit 0
+  '';
+in
+{
+  options.services.dualsenseAttenuation = {
+    enable = lib.mkEnableOption "Apply DualSense haptic attenuation on plug-in";
+
+    rumble = lib.mkOption {
+      type = lib.types.ints.between 0 7;
+      default = 3;
+      description = ''
+        Rumble (LRA) attenuation, 0-7. Higher = weaker. 3 keeps the LRAs
+        below their audible-whine threshold while leaving rumble clearly
+        perceptible. 0 disables attenuation (full strength).
+      '';
+    };
+
+    trigger = lib.mkOption {
+      type = lib.types.ints.between 0 7;
+      default = 0;
+      description = ''
+        Adaptive trigger attenuation, 0-7. Higher = weaker. 0 leaves
+        trigger feedback untouched — forza-trigger drives the triggers
+        with bounded amplitudes already, so the trigger LRAs don't
+        normally hit the audible regime.
+      '';
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    services.udev.extraRules = ''
+      # DualSense (USB)
+      ACTION=="add", SUBSYSTEM=="hidraw", ATTRS{idVendor}=="054c", ATTRS{idProduct}=="0ce6", TAG+="systemd", ENV{SYSTEMD_WANTS}+="dualsense-attenuation.service"
+      # DualSense Edge (USB)
+      ACTION=="add", SUBSYSTEM=="hidraw", ATTRS{idVendor}=="054c", ATTRS{idProduct}=="0df2", TAG+="systemd", ENV{SYSTEMD_WANTS}+="dualsense-attenuation.service"
+      # DualSense (Bluetooth)
+      ACTION=="add", SUBSYSTEM=="hidraw", KERNELS=="*054C:0CE6*", TAG+="systemd", ENV{SYSTEMD_WANTS}+="dualsense-attenuation.service"
+      # DualSense Edge (Bluetooth)
+      ACTION=="add", SUBSYSTEM=="hidraw", KERNELS=="*054C:0DF2*", TAG+="systemd", ENV{SYSTEMD_WANTS}+="dualsense-attenuation.service"
+    '';
+
+    systemd.services.dualsense-attenuation = {
+      description = "Apply DualSense rumble/trigger attenuation in controller firmware";
+      serviceConfig = {
+        Type = "oneshot";
+        ExecStart = applyScript;
+      };
+    };
+  };
+}