Amazon Kindle Fire (amazon-otter)

Contributors

 * Foldmorepaper
 * h_ro

Root and Fastboot
If the device can reach fastboot mode, the device does not need to be rooted to install recovery since the stock bootloader is already unlocked. Typically, a "Motorola factory cable" is needed to power the device into fastboot mode, but with root and fbmode utility, the device can reboot into fastboot mode without the special cable.

Rooting with saferoot
Source: https://forum.xda-developers.com/t/root-saferoot-root-for-vruemj7-mk2-and-android-4-3.2565758/#post-48392009

Booting into fastboot from Android
Source: https://forum.xda-developers.com/t/fastboot-stock-6-2-1-fastboot-mode-without-rooting-or-cables.1414832/

Custom Bootloader
A custom version of Hashcode's (2014) u-boot port with device tree support is required to boot mainline Linux kernel. The following steps are based off of h_ro's documentation repo.

Toolchain used: Linaro GCC4.9 ARMv7 Baremetal

Installing bootloader
Set the device to fastboot mode and flash the bootloader directly with fastboot.

u-boot version should appear on the top right corner when lcd menu is entered. For postmarketOS, version L2.13 or newer is required.

Custom Recovery: TWRP
Download an otter recovery image from TWRP website here.

Set the device to fastboot mode and flash the recovery with fastboot.

Installation
For more advanced installation methods, see here.

Stock Partition Layout
Output of  while in TWRP recovery:

Model: MMC M8G2FA (sd/mmc) Disk /dev/block/mmcblk0: 7734MB Sector size (logical/physical): 512B/512B Partition Table: gpt