blog: nixos-kernel-hacking: finish the rest of the article
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@@ -101,7 +101,7 @@ this patch can alternately be represented as a [Device Tree Overlay] (DTO):
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// instruct the system to only apply this overlay
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// to PinePhone Pro, and not any other devices.
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/ {
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compatible = "pine64,pinephone-pro";
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compatible = "pine64,pinephone-pro";
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};
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// address the parent node we want to patch,
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@@ -109,7 +109,7 @@ this patch can alternately be represented as a [Device Tree Overlay] (DTO):
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// this overrides `press-threshold-microvolt`
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// while leaving all other properties unchanged.
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&{/adc-keys/button-down} {
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press-threshold-microvolt = <400000>;
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press-threshold-microvolt = <400000>;
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};
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```
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@@ -155,15 +155,173 @@ then, we can ship new kernel modules by:
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### Building a Kernel Module
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TODO
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my kernel module has 3 files, which live in my nix repo inline:
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- [rk818_battery.c](https://git.uninsane.org/colin/nix-files/src/commit/4e008c34208143a489d824b288437201f7137ace/pkgs/linux-packages/rk818-charger/rk818_battery.c)
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- [rk818_battery.h](https://git.uninsane.org/colin/nix-files/src/commit/4e008c34208143a489d824b288437201f7137ace/pkgs/linux-packages/rk818-charger/rk818_battery.h)
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- [rk818_charger.c](https://git.uninsane.org/colin/nix-files/src/commit/4e008c34208143a489d824b288437201f7137ace/pkgs/linux-packages/rk818-charger/rk818_charger.c)
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these are compiled into `rk818_battery.ko` and `rk818_charger.ko` by a Makefile:
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```make
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obj-m := rk818_battery.o rk818_charger.o
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all:
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$(MAKE) -C "$(KERNEL_DIR)" M="$(PWD)" modules
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install:
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install -Dm444 rk818_battery.ko $(INSTALL_MOD_PATH)/drivers/power/supply/rk818_battery.ko
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install -Dm444 rk818_charger.ko $(INSTALL_MOD_PATH)/drivers/power/supply/rk818_charger.ko
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```
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this can be packaged for nix as so:
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```nix
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# file: pkgs/linux-packages/rk818-charger/default.nix
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{
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buildPackages,
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kernel,
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lib,
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stdenv,
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}: stdenv.mkDerivation {
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pname = "rk818-charger";
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version = "0-unstable-2024-10-01";
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src = ./.;
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hardeningDisable = [ "pic" ];
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nativeBuildInputs = kernel.moduleBuildDependencies;
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makeFlags = [
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"KERNEL_DIR=${kernel.dev}/lib/modules/${kernel.modDirVersion}/build"
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"INSTALL_MOD_PATH=$(out)/lib/modules/${kernel.modDirVersion}/kernel"
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# from pkgs/os-specific/linux/kernel/manual-config.nix:
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"O=$(buildRoot)"
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"CC=${stdenv.cc}/bin/${stdenv.cc.targetPrefix}cc"
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"HOSTCC=${buildPackages.stdenv.cc}/bin/${buildPackages.stdenv.cc.targetPrefix}cc"
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"HOSTLD=${buildPackages.stdenv.cc.bintools}/bin/${buildPackages.stdenv.cc.targetPrefix}ld"
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"ARCH=${stdenv.hostPlatform.linuxArch}"
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] ++ lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
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"CROSS_COMPILE=${stdenv.cc.targetPrefix}"
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];
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# NixOS kernel expects compressed kernel modules, so do that here.
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postInstall = ''
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find $out -name '*.ko' -exec xz {} \;
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'';
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}
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```
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then add this package to the `linuxKernel` package set:
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```nix
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{ ... }:
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{
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nixpkgs.overlays = [(self: super: {
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linuxKernel = super.linuxKernel // {
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packagesFor = kernel:
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(
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super.linuxKernel.packagesFor kernel
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).extend (kFinal: kPrev: with kFinal; {
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rk818-charger = callPackage ./pkgs/linux-packages/rk818-charger { };
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});
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};
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})];
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}
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```
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kernel modules must be built against the same kernel version
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that they'll be loaded by: this `linuxKernel` package set looks
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funny at first, but it exists to make that easier.
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your kernel module can be built like this:
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- `nix-build -A linuxPackages_6_11.rk818-charger`
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- `nix-build -A linuxPackages_6_10.rk818-charger`
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and so on, depending on which kernel you're running.
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### Deploying a Kernel Module
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TODO
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add the following to your NixOS config:
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```nix
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{ config, ... }:
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{
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# this builds our modules against the specific kernel in use by the host
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# and makes them available under /run/current-system/kernel-modules to tools like `modprobe`
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boot.extraModulePackages = [
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config.boot.kernelPackages.rk818-charger
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];
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# explicitly load the modules during stage-2 boot.
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# if they're needed earlier in the boot process, use `boot.initrd.kernelModules` instead.
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boot.kernelModules = [
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"rk818_battery"
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"rk818_charger"
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];
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}
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```
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now we've recreated the same behavior as if the kernel module had been shipped in-tree,
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but we still have to associate the driver with a specific device if we want it to do anything.
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### Device Tree + Module Integration
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TODO
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add the following Device Tree Overlay to `hardware.deviceTree.overlays`,
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as we did earlier with the battery DTO:
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```dts
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/dts-v1/;
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/plugin/;
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// apply the overlay only to PinePhone Pro; no other devices.
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/ {
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compatible = "pine64,pinephone-pro";
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};
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&{/} {
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bat: battery {
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compatible = "simple-battery";
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voltage-min-design-microvolt = <3400000>;
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voltage-max-design-microvolt = <4350000>;
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};
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};
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&rk818 {
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battery {
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// this line associates this device with the rk818-battery module
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// we just shipped
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compatible = "rockchip,rk818-battery";
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// constants were taken from the pine64-org kernel tree:
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ocv_table = <3400 3675 3689 3716 3740 3756 3768 3780
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3793 3807 3827 3853 3896 3937 3974 4007 4066
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4110 4161 4217 4308>;
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design_capacity = <2916>;
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design_qmax = <2708>;
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bat_res = <150>;
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max_input_current = <3000>;
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max_chrg_current = <2000>;
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max_chrg_voltage = <4350>;
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sleep_enter_current = <300>;
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sleep_exit_current = <300>;
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power_off_thresd = <3400>;
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zero_algorithm_vol = <3950>;
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fb_temperature = <105>;
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sample_res = <10>;
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max_soc_offset = <60>;
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energy_mode = <0>;
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monitor_sec = <5>;
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virtual_power = <0>;
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power_dc2otg = <0>;
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otg5v_suspend_enable = <1>;
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};
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charger {
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// this line associates this device with the rk818-charger module
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// we just shipped
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compatible = "rockchip,rk818-charger";
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monitored-battery = <&bat>;
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};
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};
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```
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## Patching an Upstream Kernel Module
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