#!/usr/bin/env bash

# SPDX-License-Identifier: GPL-2.0+

# How to build and boot a custom kernel
# -------------------------------------
#
# Install package dependencies
#   - RedHat-based systems
#         dnf install abootimg android-tools gcc-arm-linux-gnu 
#   - Debian-based systems
#         apt-get install abootimg fastboot gcc-8-arm-linux-gnueabihf
#
# Clone Linus's linux and the nexus-5-upstream repositories:
#
#   mkdir ~/src
#   git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
#   git clone https://github.com/masneyb/nexus-5-upstream.git
#
#   # Optional: Clone downstream MSM 3.4 sources
#   git clone https://github.com/AICP/kernel_lge_hammerhead.git linux-msm-3.4-hammerhead
#   cd ~/src/linux-msm-3.4-hammerhead
#   git am ~/src/nexus-5-upstream/out-of-tree-patches/downstream-patches/*.patch
#
# Install postmarketOS user space on the phone as described at
# https://wiki.postmarketos.org/wiki/Google_Nexus_5_(lg-hammerhead)
#
# Build and boot the upstream kernel (Use absolute paths!):
#
#   ~/src/nexus-5-upstream/build-kernel ~/src/linux
#   sudo fastboot boot ~/src/linux/arch/arm/boot/nexus5-boot.img
#
# Build and boot the downstream kernel https://github.com/AICP/kernel_lge_hammerhead. Note that
# I haven't been able to get the framebuffer to work on the downstream kernel, so you'll need
# to build a serial cable as described in UART_CABLE.md. You can clone the Raspberry Pi tools
# repo at https://github.com/raspberrypi/tools in order to get a suitable cross compiler.
#
#   export CROSS_COMPILE=/path/to/rpi/tools/arm-bcm2708/arm-rpi-4.9.3-linux-gnueabihf/bin/arm-linux-gnueabihf-
#   ~/src/nexus-5-upstream/build-kernel ~/src/linux-msm-3.4-hammerhead "" hammerhead_defconfig \
#       ~/src/linux-msm-3.4-hammerhead/arch/arm/boot/msm8974-hammerhead-rev-11.dtb ttyHSL0
#   sudo fastboot boot ~/src/linux-msm-3.4-hammerhead/arch/arm/boot/nexus5-boot.img
#
# Note that the optional second argument to build-kernel is a separate directory outside this
# repository that contains an additional directory to add to the initrd. I use this to add my
# local WiFi password and bluetooth firmware. See the .gitignore for the exact paths.

set -e

build_kernel()
{
	export ARCH=arm
	export PATH="${PATH}":"${KERNEL_SRC}"/scripts/dtc

	if [ "${CROSS_COMPILE}" = "" ] ; then
		if [ -f /usr/bin/arm-linux-gnu-gcc ] ; then
			export CROSS_COMPILE=/usr/bin/arm-linux-gnu-
		elif [ -f /usr/bin/arm-linux-gnueabihf-gcc ] ; then
			export CROSS_COMPILE=/usr/bin/arm-linux-gnueabihf-
		else
			echo "Can't setup CROSS_COMPILE environment variable"
			exit 1
		fi
	fi

	if [ "${NUM_CPUS}" = "" ] ; then
		NUM_CPUS=$(grep -c ^processor /proc/cpuinfo)
	fi

	cd "${KERNEL_SRC}"
	echo "Running 'make ${DEFCONFIG}'"
	make "${DEFCONFIG}"
	make kernelrelease

	#HAS_DT_BINDING_CHECK=$(grep ^dt_binding_check: Makefile || true)
	#if [ "${HAS_DT_BINDING_CHECK}" != "" ] ; then
	#	make dt_binding_check
	#fi

	nice -n 19 make -j "${NUM_CPUS}"

	echo "Using DTB ${DTB}"
	ZIMAGE_DTB=$(mktemp)
	cat arch/arm/boot/zImage "${DTB}" > "${ZIMAGE_DTB}"
}

generate_boot_cfg()
{
	cat > "${BOOT_CFG}" << __EOF__
	pagesize = 0x800
	kerneladdr = 0x8000
	ramdiskaddr = 0x2900000
	secondaddr = 0xf00000
	tagsaddr = 0x2700000
	name = 
	cmdline = console=tty0 console=${SERIAL_TTY},115200,n8 msm.allow_vram_carveout msm.vram=48m rootwait PMOS_NO_OUTPUT_REDIRECT
__EOF__
}

create_char_device()
{
       if [ ! -c "${1}" ] ; then
               echo "Creating ${1}"
               sudo mknod --mode="${2}" "${1}" c "${3}" "${4}"
       fi
}

generate_initrd()
{
	BASE_DIR=$(dirname "$0")
	INITRD_DIR="${BASE_DIR}/initrd"
	mkdir -p "${INITRD_DIR}/boot" "${INITRD_DIR}/dev" "${INITRD_DIR}/proc" "${INITRD_DIR}/sys" \
	         "${INITRD_DIR}/sysroot" "${INITRD_DIR}/tmp" "${INITRD_DIR}/usr/bin"

	sed "s/__SERIAL_TTY__/${SERIAL_TTY}/g" "${INITRD_DIR}/copy-to-root-fs/etc/inittab.template" > \
		"${INITRD_DIR}"/copy-to-root-fs/etc/inittab

	if [ ! -e "${INITRD_DIR}"/bin/sh ] ; then
		pushd "${INITRD_DIR}"/bin/
		ln -s busybox sh
		popd
	fi

	create_char_device "${INITRD_DIR}"/dev/null 0666 1 3
	create_char_device "${INITRD_DIR}"/dev/random 0644 1 8
	create_char_device "${INITRD_DIR}"/dev/urandom 0644 1 9

	if [ "${EXTRA_INITRD}" != "" ] ; then
		cp -dpR "${EXTRA_INITRD}"/* "${INITRD_DIR}"
	fi

	rm -rf "${INITRD_DIR}/lib/modules"
	make INSTALL_MOD_PATH="${INITRD_DIR}" modules_install || true
	cd "${INITRD_DIR}"
	find . | grep -v \.placeholder | cpio --create --format="newc" --quiet > "${INITRD}"
	# To extract: cpio -idm --quiet < initrd.img
}

export KERNEL_SRC="$1"
export EXTRA_INITRD="$2"
export DEFCONFIG="${3:-qcom_defconfig}"
export DTB="${4:-arch/arm/boot/dts/qcom-msm8974-lge-nexus5-hammerhead.dtb}"
export SERIAL_TTY="${5:-ttyMSM0}" # downstream kernel uses ttyHSL0; upstream is ttyMSM0

if [ "${KERNEL_SRC}" = "" ] ; then
	echo "$0 <kernel source tree> [ <defconfig> ] [ dtb ] [ serial tty ]"
	exit 1
fi

build_kernel

BOOT_CFG=$(mktemp)
generate_boot_cfg

INITRD=$(mktemp)
generate_initrd

ABOOT_IMG="${KERNEL_SRC}"/arch/arm/boot/nexus5-boot.img
abootimg --create "${ABOOT_IMG}" -f "${BOOT_CFG}" -k "${ZIMAGE_DTB}" -r "${INITRD}"

rm -f "${BOOT_CFG}" "${INITRD}" "${ZIMAGE_DTB}"

ls -lh "${ABOOT_IMG}"
echo "Hint: If the image above is too big, then be sure that CONFIG_MEDIA_SUPPORT_FILTER"
echo "is enabled."
echo ""
echo "Run to boot the kernel without flashing the boot partition:"
echo "    sudo fastboot boot ${ABOOT_IMG}"
echo ""
echo "Run to flash the kernel on the boot paritition:"
echo "    sudo fastboot flash boot ${ABOOT_IMG}"