alsa-ucm-pinephone-pmos: prefer the earpiece over the "internal speaker"

hosts/common/programs/alsa-ucm-conf/default.nix

@@ -37,7 +37,9 @@ in
     # - headphones work
     # - "internal earpiece" works
     # - "internal speaker" is silent (maybe hardware issue)
-    packageUnwrapped = pkgs.alsa-ucm-pinephone-pmos;  #< TODO: plumb `preferEarpiece`
+    packageUnwrapped = pkgs.alsa-ucm-pinephone-pmos.override {
+      inherit (cfg.config) preferEarpiece;
+    };
 
     sandbox.enable = false;  #< only provides $out/share/alsa
 

pkgs/additional/alsa-ucm-pinephone-pmos/default.nix

@@ -1,7 +1,9 @@
 # see: https://gitlab.com/postmarketOS/pmaports/-/tree/master/device/main/device-pine64-pinephone/
 # - APKBUILD and ucm/ files
 { alsa-ucm-conf
+, lib
 , fetchFromGitLab
+, preferEarpiece ? false
 }:
 let
   pmaports = fetchFromGitLab {
@@ -20,5 +22,11 @@ in alsa-ucm-conf.overrideAttrs (upstream: {
     mkdir -p $out/share/alsa/ucm2/conf.d/simple-card
     ln -sf $out/share/alsa/ucm2/PinePhone/PinePhone.conf \
       $out/share/alsa/ucm2/conf.d/simple-card/PinePhone.conf
+  '' + lib.optionalString preferEarpiece ''
+    # decrease the priority of the internal speaker so that sounds are routed
+    # to the earpiece by default.
+    # this is just personal preference.
+    substituteInPlace $out/share/alsa/ucm2/PinePhone/{HiFi.conf,VoiceCall.conf} \
+      --replace-fail 'PlaybackPriority 300' 'PlaybackPriority 100'
   '';
 })