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)

Apple M1 Ultra SoC (t6002)

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

$ 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

$ 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.

SoC	Base Address
M1 (t8103)	0x235200000
M1 Pro/Max/Ultra (t6000/t6001/t6002)	0x39b200000