factor out serial console device choice

This commit generalizes the selection and activation of the serial
console by promoting it to a top-level package-set member.

The top-level package set is starting to attract clutter, so I will
soon be moving all the non-package constitutents into a `config`
attrset.

src/coreboot/default.nix

@@ -6,7 +6,7 @@
 , initramfs_image    # path to the initramfs `cpio` archive
 , iasl               ? null # a specific iasl to use, if needed
 , console_loglevel   ? "7"
-, linux-command-line ? ""
+, linux-command-line
 }:
 let
   version = "4.9";

src/default.nix

@@ -17,6 +17,13 @@ let
 
       coreboot-toolchain = final.callPackage ./coreboot-toolchain { };
 
+      # TODO(amjoseph): move this into a `config` attrset
+      console-device = throw "platforms must override this (example: \"ttyS0\")";
+      console-parameters = "115200n8";
+      linux-command-line =
+        let console = "${final.console-device},${final.console-parameters}";
+        in "console=${console} earlyprintk=${console}";
+
       iasl_20180531 = final.nixpkgsOnBuildForBuild.callPackage ./coreboot/iasl_20180531 { };
       coreboot      = final.callPackage ./coreboot {
         initramfs_image = final.initramfs;

src/platform/am1i/coreboot.config

@@ -96,7 +96,6 @@ CONFIG_TTYS0_BASE=0x3f8
 # this is the back-panel connector, which exists only on the "more back-panel stuff" board variant
 #CONFIG_UART_FOR_CONSOLE=1
 #CONFIG_TTYS0_BASE=0x2f8
-#CONFIG_LINUX_COMMAND_LINE="console=ttyS1,115200n8"
 
 CONFIG_LINUX_INITRD=""
 

src/platform/am1i/default.nix

@@ -16,13 +16,14 @@
         '';
       });
 
+    console-device = "ttyS0";
+
     coreboot = final.lib.makeOverridable (prev.coreboot.override {
       iasl = final.iasl_20180531;
       payload = "${final.kernel}/bzImage";
       coreboot-toolchain = with final.coreboot-toolchain; [ x64 i386 ];
       fmap = ./custom.fmap;
       config = ./coreboot.config;
-      linux-command-line="console=ttyS0,115200n8";
     }).overrideAttrs (a: {
       /*
       postConfigure = (a.postConfigure or "") + ''

src/platform/kevin/default.nix

@@ -59,6 +59,11 @@ in {
       modules = modules_insmod ++ modules_noinsmod;
     };
 
+    # these pins are on the motherboard's "servo connector"; you'll
+    # need a breakout board like this:
+    # https://github.com/SolidHal/servo-v2-breakout-board
+    console-device = "ttyS2";
+
     coreboot =
       let atf = final.nixpkgsOnBuildForHost.callPackage (import ./atf) {
             buildArmTrustedFirmware = (final.nixpkgsOnBuildForHost.callPackage (import <nixpkgs/pkgs/misc/arm-trusted-firmware>) {
@@ -74,7 +79,6 @@ in {
         fmap = ./custom.fmap;
         config = ./coreboot.config;
         coreboot-toolchain = with final.coreboot-toolchain; [ aarch64 ];
-        linux-command-line="console=ttyS2,115200n8";
       }).overrideAttrs (a: {
         postConfigure = ''
           echo CONFIG_ARM64_BL31_EXTERNAL_FILE=\"${atf}/bl31.elf\" >> .config

src/platform/kgpe/default.nix

@@ -41,13 +41,15 @@
     # TODO: use a NixOS-style structuredConfig for this.
     cmos-default = null;
 
+    console-device = "ttyS0";   # the DB9 connector on the rear panel
+    #console-device = "ttyS1";  # the IDC header on the motherboard
+
     coreboot = final.lib.makeOverridable (prev.coreboot.override {
       iasl = final.iasl_20180531;
       payload = "${final.kernel}/bzImage";
       fmap = ./custom.fmap;
       config = ./coreboot.config;
       coreboot-toolchain = with final.coreboot-toolchain; [ x64 i386 ];
-      linux-command-line = "console=ttyS1,115200n8";
     }).overrideAttrs (a: {
       postConfigure = if final.microcode-blob != null then ''
         echo CONFIG_CPU_MICROCODE_MULTIPLE_FILES=y >> .config