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doc: ARMv8: add README.pine64

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Since we lack information about the DRAM initialization for the
Allwinner A64 SoC, booting any A64 based board like the Pine64 is a bit
involved at the moment.
Add a README file to explain the process.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
[trini: Move to board/sunxi/ from doc/]
Signed-off-by: Tom Rini <trini@konsulko.com>
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Andre Przywara 2016-07-08 15:25:23 +01:00 committed by Tom Rini
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commit a868598a48
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Pine64 board README
====================
The Pine64(+) is a single board computer equipped with an AArch64 capable ARMv8
compliant Allwinner A64 SoC.
This chip has ARM Cortex A-53 cores and thus can run both in AArch32
(compatible to 32-bit ARMv7) and AArch64 modes. Upon reset the SoC starts
in AArch32 mode and executes 32-bit code from the Boot ROM (BROM).
This has some implications on U-Boot.
Quick start
============
- Get hold of a boot0.img file (see below for more details).
- Get the boot0img tool source from the tools directory in [1] and compile
that on your host.
- Build U-Boot:
$ export CROSS_COMPILE=aarch64-linux-gnu-
$ make pine64_plus_defconfig
$ make
- You also need a compiled ARM Trusted Firmware (ATF) binary. Checkout the
"allwinner" branch from the github repository [2] and build it:
$ export CROSS_COMPILE=aarch64-linux-gnu-
$ make PLAT=sun50iw1p1 DEBUG=1 bl31
The resulting binary is build/sun50iw1p1/debug/bl31.bin.
Now put an empty (or disposable) micro SD card in your card reader and learn
its device file name, replacing /dev/sd<x> below with the result (that could
be /dev/mmcblk<x> as well):
$ ./boot0img --device /dev/sd<x> -e -u u-boot.bin -B boot0.img \
-d trampoline64:0x44000 -s bl31.bin -a 0x44008 -p 100
(either copying the respective files to the working directory or specifying
the paths directly)
This will create a new partition table (with a 100 MB FAT boot partition),
copies boot0.img, ATF and U-Boot to the proper locations on the SD card and
will fill in the magic Allwinner header to be recognized by boot0.
Prefix the above call with "sudo" if you don't have write access to the
uSD card. You can also use "-o output.img" instead of "--device /dev/sd<x>"
to create an image file and "dd" that to the uSD card.
Omitting the "-p" option will skip the partition table.
Now put this uSD card in the board and power it on. You should be greeted by
the U-Boot prompt.
Main U-Boot
============
The main U-Boot proper is a real 64-bit ARMv8 port and runs entirely in the
64-bit AArch64 mode. It can load any AArch64 code, EFI applications or arm64
Linux kernel images (often named "Image") using the booti command.
Launching 32-bit code and kernels is technically possible, though not without
drawbacks (or hacks to avoid them) and currently not implemented.
SPL support
============
The main task of the SPL support is to bring up the DRAM controller and make
DRAM actually accessible. At the moment there is no documentation or source
code available which would do this.
There are currently two ways to overcome this situation: using a tainted 32-bit
SPL (involving some hacks and resulting in a non-redistributable binary, thus
not described here) or using the Allwinner boot0 blob.
boot0 method
-------------
boot0 is Allwiner's secondary program loader and it can be used as some kind
of SPL replacement to get U-Boot up and running.
The binary is a 32 KByte blob and contained on every Pine64 image distributed
so far. It can be easily extracted from a micro SD card or an image file:
# dd if=/dev/sd<x> of=boot0.bin bs=8k skip=1 count=4
where /dev/sd<x> is the device name of the uSD card or the name of the image
file. Apparently Allwinner allows re-distribution of this proprietary code
as-is.
For the time being this boot0 blob is the only redistributable way of making
U-Boot work on the Pine64. Beside loading the various parts of the (original)
firmware it also switches the core into AArch64 mode.
The original boot0 code looks for U-Boot at a certain place on an uSD card
(at 19096 KB), also it expects a header with magic bytes and a checksum.
There is a tool called boot0img[1] which takes a boot0.bin image and a compiled
U-Boot binary (plus other binaries) and will populate that header accordingly.
To make space for the magic header, the pine64_plus_defconfig will make sure
there is sufficient space at the beginning of the U-Boot binary.
boot0img will also take care of putting the different binaries at the right
places on the uSD card and works around unused, but mandatory parts by using
trampoline code. See the output of "boot0img -h" for more information.
boot0img can also patch boot0 to avoid loading U-Boot from 19MB, instead
fetching it from just behind the boot0 binary (-B option).
FEL boot
=========
FEL is the name of the Allwinner defined USB boot protocol built-in the
mask ROM of most Allwinner SoCs. It allows to bootstrap a board solely
by using the USB-OTG interface and a host port on another computer.
Since FEL boot does not work with boot0, it requires the libdram hack, which
is not described here.
[1] https://github.com/apritzel/pine64/
[2] https://github.com/apritzel/arm-trusted-firmware.git