moby: ship megis rt5640 sound driver (experimental. it still boots, but pipewire/wireplumber still crash-loops)

hosts/modules/hal/pine64-pinephone-pro/default.nix

@@ -189,7 +189,8 @@ in
 
     boot.extraModulePackages = [
       config.boot.kernelPackages.rk818-charger  #< rk818 battery/charger isn't mainline as of 2024-10-01
-      config.boot.kernelPackages.imx258  #< mainline imx258 camera driver has some power-on and data rate issues on PPP
+      config.boot.kernelPackages.imx258  #< mainline imx258 camera driver has some power-on issues on PPP  (imx258 1-001a: Error reading reg 0x0016: -6)
+      config.boot.kernelPackages.rt5640  #< mainline rt5640 generally works. possibly bad interplay with the imx258 camera, that i'm debugging, so use megi's patched rt5640.
     ];
 
     # default nixos behavior is to error if a kernel module is provided by more than one package.

pkgs/linux-packages/rt5640/Makefile

@@ -0,0 +1,7 @@
+obj-m := snd-soc-rt5640.o
+
+all:
+	$(MAKE) -C "$(KERNEL_DIR)" M="$(PWD)" modules
+install:
+	install -Dm444 snd-soc-rt5640.ko $(INSTALL_MOD_PATH)/sound/soc/codecs/snd-soc-rt5640.ko
+

pkgs/linux-packages/rt5640/package.nix

@@ -0,0 +1,45 @@
+# C code is taken from megi's kernel tree.
+# this is a patched version of mainline driver.
+# notably, it resolves some errors like "rt5640 1-001c: ASoC: error at snd_soc_dai_set_sysclk on rt5640-aif1: -22".
+#
+# the driver source lives at sound/soc/codecs/rt5640.c; it's renamed to sound-soc-rt5640 during build
+{
+  buildPackages,
+  kernel,
+  lib,
+  stdenv,
+}:
+
+stdenv.mkDerivation {
+  pname = "rt5640";
+  version = "0-unstable-2024-02-21";
+
+  src = ./.;
+
+  hardeningDisable = [ "pic" ];
+  nativeBuildInputs = kernel.moduleBuildDependencies;
+
+  makeFlags = [
+    # "KERNELRELEASE=${kernel.modDirVersion}"
+    "KERNEL_DIR=${kernel.dev}/lib/modules/${kernel.modDirVersion}/build"
+    "INSTALL_MOD_PATH=$(out)/lib/modules/${kernel.modDirVersion}/kernel"
+    # from <repo:nixos/nixpkgs:pkgs/os-specific/linux/kernel/manual-config.nix>
+    "O=$(buildRoot)"
+    "CC=${stdenv.cc}/bin/${stdenv.cc.targetPrefix}cc"
+    "HOSTCC=${buildPackages.stdenv.cc}/bin/${buildPackages.stdenv.cc.targetPrefix}cc"
+    "HOSTLD=${buildPackages.stdenv.cc.bintools}/bin/${buildPackages.stdenv.cc.targetPrefix}ld"
+    "ARCH=${stdenv.hostPlatform.linuxArch}"
+  ] ++ lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
+    "CROSS_COMPILE=${stdenv.cc.targetPrefix}"
+  ];
+
+  # the modules shipped in-tree are .xz, so if i want to replace those i need to also xz this module:
+  postInstall = ''
+    find $out -name '*.ko' -exec xz {} \;
+  '';
+
+  passthru.moduleNames = [
+    "sound-soc-rt5640"    #< mainline, patched module
+  ];
+}
+

pkgs/linux-packages/rt5640/rl6231.h

@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * rl6231.h - RL6231 class device shared support
+ *
+ * Copyright 2014 Realtek Semiconductor Corp.
+ *
+ * Author: Oder Chiou <oder_chiou@realtek.com>
+ */
+
+#ifndef __RL6231_H__
+#define __RL6231_H__
+
+#define RL6231_PLL_INP_MAX	50000000
+#define RL6231_PLL_INP_MIN	256000
+#define RL6231_PLL_N_MAX	0x1ff
+#define RL6231_PLL_K_MAX	0x1f
+#define RL6231_PLL_M_MAX	0xf
+
+struct rl6231_pll_code {
+	bool m_bp; /* Indicates bypass m code or not. */
+	bool k_bp; /* Indicates bypass k code or not. */
+	int m_code;
+	int n_code;
+	int k_code;
+};
+
+int rl6231_calc_dmic_clk(int rate);
+int rl6231_pll_calc(const unsigned int freq_in,
+	const unsigned int freq_out, struct rl6231_pll_code *pll_code);
+int rl6231_get_clk_info(int sclk, int rate);
+int rl6231_get_pre_div(struct regmap *map, unsigned int reg, int sft);
+
+#endif /* __RL6231_H__ */