The device tree on Apple silicon devices is passed from a previous
bootloader stage. The bootloader fills in dynamic information so
u-boot can not use its own device tree.
As documented in doc/board/apple/m1.rst it is possible to build boot
bundles (bootloader + device tree + gzipped u-boot binary). These are
useful for testing.
Instead of using u-boot's own device trees for M1 (t8103) devices use
upstream device trees from dts/upstream/src/arm64/apple. The u-boot
device trees have not seen updates since 2022. The upstream linux device
trees have feature parity for the M1 devices. In addition linux has
device trees for M1 Pro/Max/Ultra, M2 and M2 Pro/Max/Ultra devices.
Keep t8103-j274 as default device tree to avoid further updates.

Signed-off-by: Janne Grunau <j@jannau.net>
Acked-by: Mark Kettenis <kettenis@openbsd.org>

These SoCs are supported since 2022/2023 but were never added to the
documentation. The devices very similar to the equivalent M1 devices.
The biggest difference is that the M2 and M2 Pro/Max based laptops no
longer use SPI for the keyboard.

Signed-off-by: Janne Grunau <j@jannau.net>
Acked-by: Mark Kettenis <kettenis@openbsd.org>

U-Boot now supports the M1 Ultra SoC as found in the new Mac Studio.

Signed-off-by: Mark Kettenis <kettenis@openbsd.org>

U-Boot now supports NVMe storage and on the laptop models, the
SPI keyboard.  Since we now disable the debug console by default
provide instructions on how the enable the debug console including
a table listing the appropriate UART base address for each of the
supported SoCs.

Signed-off-by: Mark Kettenis <kettenis@openbsd.org>

Provide preliminary instructions on how to get U-Boot to run on
Apple Silicon Macs.

Signed-off-by: Mark Kettenis <kettenis@openbsd.org>
Reviewed-by: Simon Glass <sjg@chromium.org>