payloads/external/LinuxBoot: Adopt u-root change

The u-root toolkit dropped the original uinit bootloader in the master
branch and respectively the systemboot-option in templates.go. In
consequence the LinuxBoot builds will boot into the u-root shell and
waiting for input. This commit enables the reuse of the -uinitcmd flag
to specify a command, which runs after the u-root init-process.

Systemboot as a bootloader wrapper will mimic a BIOS/UEFI boot device
selection. Other preselections, i.e. stboot and boot2 are implemented as
well. Custom strings or programs can be set as well, but they cannot
contain program flags. E.g. 'fbnetboot -class linuxboot' will not work,
because they aren't symlinkable.

This commit and its respective LinuxBoot builds with systemboot, none
and one custom option have been tested successfully on a UP squared
single board computer with the intended behavior.

Change-Id: I4ac3409040ea77a1836f90f43fba07d2cd05a952
Signed-off-by: Patrik Tesarik <mail@patrik-tesarik.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/40316
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Christian Walter <christian.walter@9elements.com>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

payloads/external/LinuxBoot/Kconfig

@@ -258,6 +258,61 @@ config LINUXBOOT_UROOT_COMMANDS
 	  List of additional modules to include,
 	  separated by space. (default "boot coreboot-app")
 
+if LINUXBOOT_UROOT_MAIN
+
+choice
+	prompt "Choose a specific bootloader"
+	default SPECIFIC_BOOTLOADER_NONE
+	help
+	  Specify a bootloader which starts after u-root init. It will be a symlink
+	  to /bin/uinit. Default: None
+
+config SPECIFIC_BOOTLOADER_NONE
+	bool "none"
+	help
+	  Leave u-root to decide which bootloaders to load first after init, if
+	  any at all. Most likely u-root will start into the defined u-root shell.
+
+config SPECIFIC_BOOTLOADER_SYSTEMBOOT
+	bool "systemboot"
+	help
+	  If systemboot has been used as a bootloader wrapper in the past,
+	  enable this option. It will invoke -uinitcmd=systemboot and result in
+	  a BIOS/UEFI BDS boot behavior.
+
+config SPECIFIC_BOOTLOADER_BOOT2
+	bool "boot2"
+
+config SPECIFIC_BOOTLOADER_PXEBOOT
+	bool "pxeboot"
+
+config SPECIFIC_BOOTLOADER_STBOOT
+	bool "stboot"
+
+config SPECIFIC_BOOTLOADER_CUSTOM
+	bool "custom"
+
+endchoice
+
+config SPECIFIC_BOOTLOADER_CUSTOM_CMD
+	string "Specify a custom program to start"
+	depends on SPECIFIC_BOOTLOADER_CUSTOM
+	help
+	  This option will symlink the input to /bin/unit which will set it as the
+	  first boot program after the u-root init. Program flags are not
+	  symlinkable.
+
+config LINUXBOOT_UROOT_UINITCMD
+	string
+	default "" if SPECIFIC_BOOTLOADER_NONE
+	default "systemboot" if SPECIFIC_BOOTLOADER_SYSTEMBOOT
+	default "boot2" if SPECIFIC_BOOTLOADER_BOOT2
+	default "pxeboot" if SPECIFIC_BOOTLOADER_PXEBOOT
+	default "stboot" if SPECIFIC_BOOTLOADER_STBOOT
+	default SPECIFIC_BOOTLOADER_CUSTOM_CMD if SPECIFIC_BOOTLOADER_CUSTOM
+
+endif #LINUXBOOT_UROOT_MAIN
+
 endif #LINUXBOOT_UROOT
 
 endif #LINUXBOOT_BUILD_INITRAMFS

payloads/external/LinuxBoot/targets/u-root.mk

@@ -15,6 +15,7 @@ go_version_minor=$(shell echo $(go_version) |  sed -nr 's/^([0-9]+)\.([0-9]+)\.?
 
 uroot_args+=-build=$(CONFIG_LINUXBOOT_UROOT_FORMAT)
 uroot_args+=-initcmd $(CONFIG_LINUXBOOT_UROOT_INITCMD)
+uroot_args+=-uinitcmd=$(CONFIG_LINUXBOOT_UROOT_UINITCMD)
 uroot_args+=-defaultsh $(CONFIG_LINUXBOOT_UROOT_SHELL)
 ifneq (CONFIG_LINUXBOOT_UROOT_FILES,)
 uroot_args+=$(foreach file,$(CONFIG_LINUXBOOT_UROOT_FILES),-files $(PWD)/$(file))

payloads/external/Makefile.inc

@@ -343,6 +343,7 @@ linuxboot:
 		CONFIG_LINUXBOOT_UROOT_VERSION=$(CONFIG_LINUXBOOT_UROOT_VERSION) \
 		CONFIG_LINUXBOOT_UROOT_FORMAT=$(CONFIG_LINUXBOOT_UROOT_FORMAT) \
 		CONFIG_LINUXBOOT_UROOT_INITCMD=$(CONFIG_LINUXBOOT_UROOT_INITCMD) \
+		CONFIG_LINUXBOOT_UROOT_UINITCMD=$(CONFIG_LINUXBOOT_UROOT_UINITCMD)\
 		CONFIG_LINUXBOOT_UROOT_SHELL=$(CONFIG_LINUXBOOT_UROOT_SHELL) \
 		CONFIG_LINUXBOOT_UROOT_COMMANDS=$(CONFIG_LINUXBOOT_UROOT_COMMANDS) \
 		CONFIG_LINUXBOOT_UROOT_FILES=$(CONFIG_LINUXBOOT_UROOT_FILES) \