.. SPDX-License-Identifier: GPL-2.0+

U-Boot for Apple Silicon Macs
=============================

Allows Apple Silicon Macs to boot U-Boot via the m1n1 bootloader
developed by the Asahi Linux project.  At this point the machines with
the following SoCs work:

 - Apple M1 SoC (t8103)
 - Apple M1 Pro SoC (t6000)
 - Apple M1 Max SoC (t6001)

On these SoCs the following hardware is supported:

 - S5L serial port
 - SPI keyboard (on laptops)
 - Framebuffer
 - NVMe storage
 - USB 3.1 Type-C ports

Device trees are currently provided for the M1 Mac mini (2020, J274),
M1 MacBook Pro 13" (2020, J293), M1 MacBook Air (2020, J313) and M1
iMac (2021, J456/J457).

Building U-Boot
---------------

.. code-block:: bash

    $ export CROSS_COMPILE=aarch64-none-elf-
    $ make apple_m1_defconfig
    $ make

This will build ``u-boot-nodtb.bin`` as well as devices trees for some
of the supported machines.  These device trees can be found in the
``arch/arm/dts`` subdirectory of your build.

Image creation
--------------

In order to run U-Boot on an Apple Silicon Mac, U-Boot has to be used
as a payload for the m1n1 bootloader.  Instructions for building m1n1
can be found here:

    https://github.com/AsahiLinux/docs/wiki/SW%3Am1n1

.. code-block:: bash

    $ cat m1n1.macho t8103-j274.dtb u-boot-nodtb.bin > u-boot.macho

This uses ``u-boot-nodtb.bin`` as the device tree is passed to U-Boot
by m1n1 after making some adjustments.

Image installation
------------------

Instructions on how to install U-Boot on your Mac can be found at:

    https://github.com/AsahiLinux/docs/wiki/Developer-Quickstart

Just replace ``m1n1.macho`` with ``u-boot.macho`` in the instructions.

Debug UART
----------

Since the base address of the UART is SoC-dependent, the debug UART is
not enabled by default.  To enable the debug UART the base address
needs to be adjusted and the CONFIG_DEBUG_UART option needs to be
enabled.  The table below gives the correct base address for the
supported SoCs.

.. list-table::
   :widths: 32 16
   :header-rows: 1

   * - SoC
     - Base Address
   * - M1 (t8103)
     - 0x235200000
   * - M1 Pro/Max (t6000/t6001)
     - 0x39b200000
