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docs: Add documentation about dynamic firmware

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This patch adds documenation about dynamic firmware.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>
This commit is contained in:
Anup Patel
2019-04-29 12:50:33 +05:30
committed by Anup Patel
parent a4c2f50b64
commit 392749f633
2 changed files with 51 additions and 3 deletions
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docs/firmware/fw_dynamic.md Normal file
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OpenSBI Firmware with Dynamic Information *FW_DYNAMIC*
======================================================
OpenSBI **firmware with dynamic info (FW_DYNAMIC)** is a firmware which gets
information about next booting stage (e.g. a bootloader or an OS) and runtime
OpenSBI library options from previous booting stage.
The previous booting stage will pass information to *FW_DYNAMIC* by creating
*struct fw_dynamic_info* in memory and passing it's address to *FW_DYNAMIC*
via *a2* register of RISC-V CPU.
A *FW_DYNAMIC* firmware is particularly useful when the booting stage executed
prior to OpenSBI firmware is capable of loading both the OpenSBI firmware and
the booting stage binary to follow OpenSBI firmware.
*FW_DYNAMIC* Compilation
------------------------
A platform can enable *FW_DYNAMIC* firmware using any of the following methods.
1. Specifying `FW_DYNAMIC=y` on the top level `make` command line.
2. Specifying `FW_DYNAMIC=y` in the target platform *config.mk* configuration
file.
The compiled *FW_DYNAMIC* firmware ELF file is named *fw_dynamic.elf*. It's
expanded image file is *fw_dynamic.bin*. Both files are created in the platform
specific build directory under the *build/platform/<platform_subdir>/firmware*
directory.
*FW_DYNAMIC* Firmware Configuration Options
-------------------------------------------
The *FW_DYNAMIC* firmware does not requires any platform specific configuration
parameters because all required information is passed by previous booting stage
at runtime via *struct fw_dynamic_info*.