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doc: allwinner: Reorder sections, document memory mapping 

Update the Allwinner platform documentation.
Reorder the section, to have the build instructions first, followed by
hints about the installation.

Add some ASCII art about the layout of our virtual memory map, which
uses a non-trivial condensed virtual address space.

Change-Id: Iaaa79b4366012394e15e4c1b26c212b5efb6ed6a
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
This commit is contained in:
Andre Przywara 2020-12-11 21:29:31 +00:00
parent 9ad1031408
commit fe90f9aecf
1 changed files with 52 additions and 16 deletions
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68
docs/plat/allwinner.rst
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@ -5,22 +5,8 @@ Trusted Firmware-A (TF-A) implements the EL3 firmware layer for Allwinner
SoCs with ARMv8 cores. Only BL31 is used to provide proper EL3 setup and
PSCI runtime services.
U-Boot's SPL acts as a loader, loading both BL31 and BL33 (typically U-Boot).
Loading is done from SD card, eMMC or SPI flash, also via an USB debug
interface (FEL).
BL31 lives in SRAM A2, which is documented to be accessible from secure
world only.
Current limitations:
- Missing PMIC support
After building bl31.bin, the binary must be fed to the U-Boot build system
to include it in the FIT image that the SPL loader will process.
bl31.bin can be either copied (or sym-linked) into U-Boot's root directory,
or the environment variable BL31 must contain the binary's path.
See the respective `U-Boot documentation`_ for more details.
Building TF-A
-------------
To build for machines with an A64 or H5 SoC:
@ -34,8 +20,58 @@ To build for machines with an H6 SoC:
make CROSS_COMPILE=aarch64-linux-gnu- PLAT=sun50i_h6 DEBUG=1 bl31
Installation
------------
U-Boot's SPL acts as a loader, loading both BL31 and BL33 (typically U-Boot).
Loading is done from SD card, eMMC or SPI flash, also via an USB debug
interface (FEL).
After building bl31.bin, the binary must be fed to the U-Boot build system
to include it in the FIT image that the SPL loader will process.
bl31.bin can be either copied (or sym-linked) into U-Boot's root directory,
or the environment variable BL31 must contain the binary's path.
See the respective `U-Boot documentation`_ for more details.
.. _U-Boot documentation: https://gitlab.denx.de/u-boot/u-boot/-/blob/master/board/sunxi/README.sunxi64
Memory layout
-------------
A64, H5 and H6 SoCs
~~~~~~~~~~~~~~~~~~~
BL31 lives in SRAM A2, which is documented to be accessible from secure
world only. Since this SRAM region is very limited (48 KB), we take
several measures to reduce memory consumption. One of them is to confine
BL31 to only 28 bits of virtual address space, which reduces the number
of required page tables (each occupying 4KB of memory).
The mapping we use on those SoCs is as follows:
::
0 64K 16M 1GB 1G+160M physical address
+-+------+-+---+------+--...---+-------+----+------+----------
|B| |S|///| |//...///| |////| |
|R| SRAM |C|///| dev |//...///| (sec) |////| BL33 | DRAM ...
|O| |P|///| MMIO |//...///| DRAM |////| |
|M| | |///| |//...///| (32M) |////| |
+-+------+-+---+------+--...---+-------+----+------+----------
| | | | | | / / / /
| | | | | | / / / /
| | | | | | / / / /
| | | | | | / // /
| | | | | | / / /
+-+------+-+---+------+--+-------+------+
|B| |S|///| |//| | |
|R| SRAM |C|///| dev |//| sec | BL33 |
|O| |P|///| MMIO |//| DRAM | |
|M| | |///| |//| | |
+-+------+-+---+------+--+-------+------+
0 64K 16M 160M 192M 256M virtual address
Trusted OS dispatcher
---------------------