lk2nd is a bootloader for Qualcomm MSM devices, based on the CodeAurora Little Kernel fork. It provides an Android Fastboot interface on devices where the stock bootloader does not provide Fastboot (e.g. Samsung).

lk2nd does not replace the stock bootloader. It is packaged into an Android boot image and then loaded by the stock bootloader as a "secondary" bootloader. The real Android boot image is placed into the boot partition with 1 MB offset, and then loaded by lk2nd.

• MSM8952 (MSM8940)
• MSM8953 (SDM450,SDM625,SDM626)
• SDM632

• Motorola Moto G4 Play (harpia)
• Samsung Galaxy A3 (2015) - SM-A300FU
• Samsung Galaxy A5 (2015) - SM-A500FU
• Samsung Galaxy J5 (2016) - SM-J510FN
• Samsung Galaxy S4 Mini Value Edition - GT-I9195I
• Samsung Galaxy Tab A 8.0 LTE (2015) - SM-T357W
• Samsung Galaxy Tab A 9.7 WiFi (2015) - SM-T550
• Wileyfox Swift
• Samsung Galaxy A6+ (2018) - SM-A605FN
• Xiaomi Redmi 4X - santoni
• Xiaomi Redmi Note 4X Snapdragon - mido
• Xiaomi Redmi Note 5 / 5 Plus Snapdragon - vince
• Motorola Moto G7 Power - ocean
• Xiaomi Mi A2 Lite - daisy
• Xiaomi Mi A1 - tissot
• XIaomi Mi A2 Lite - daisy

1. Download lk2nd.img (as of now there's no build available so you'll need to build it yourself.)
2. Flash lk2nd.img using the stock flashing procedure:

• Fastboot: fastboot flash boot lk2nd.img
• Samsung: heimdall flash --BOOT lk2nd.img

lk2nd provides the standard Android fastboot protocol for flashing/booting Android boot images.

Press Volume Down while booting to enter Fastboot mode. Press Volume Up while booting to boot into Recovery mode.

Note: If your stock bootloader uses the same key combinations, you need to wait a bit before pressing the volume keys. Usually, waiting until the screen turns on and/or the device vibrates should be enough to make the stock bootloader ignore the keys.

fastboot flash lk2nd lk2nd.img can be used to update lk2nd directory from its fastboot interface.

Note: fastboot flash boot boot.img will flash the actual boot image with 1 MB offset into the boot partition. This is done to avoid replacing lk2nd (since it is also booted from the boot partition).

Other fastboot commands work normally.

$ make TOOLCHAIN_PREFIX=arm-none-eabi- <SoC>-secondary

Requirements:

• ARM (32 bit) GCC tool chain
  • Arch Linux: arm-none-eabi-gcc
• Device Tree Compiler
  • Arch Linux: dtc

Replace TOOLCHAIN_PREFIX with the path to your tool chain. lk2nd.img is built and placed into build-<SoC>-secondary/lk2nd.img.

• Add a simple device tree to dts/. You just need model and the qcom,msm-id/qcom,board-id from downstream.

• Cherry-pick changes
• Make some changes
• Add secondary project config

(TODO: Document this properly)

Ping minecrell/Mis012/uknown/gavodavo on #postmarketos-mainline.