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docs/firmware: Update FW_JUMP documentation

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Reformatting, typos, and various corrections.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
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Damien Le Moal 2019-01-23 16:00:35 +09:00 • committed by Anup Patel
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docs/firmware/fw_jump.md
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OpenSBI Firmware with Jump Address (FW_JUMP)
OpenSBI Firmware with Jump Address *FW_JUMP*
============================================
The **OpenSBI firmware with Jump Address (FW_JUMP)** is a
firmware which only know the address of next booting stage
(i.e. bootloader/kernel).
OpenSBI **firmware with Jump Address (FW_JUMP)** is a firmware which only
handles the address of the next booting stage entry, e.g. a bootloader or an OS
kernel, without directly including the binary code for this next stage.
This **FW_JUMP** firmware is particularly useful when booting
stage prior to OpenSBI firmware is capable of loading OpenSBI
firmware and booting stage after OpenSBI firmware separately.
A *FW_JUMP* 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.
How to Enable?
--------------
*FW_JUMP* Compilation
---------------------
The **FW_JUMP** firmware can be enabled by any of the following
methods:
A platform *FW_JUMP* firmware can be enabled by any of the following methods.
1. Passing `FW_JUMP=y` command-line parameter to
top-level `make`
2. Setting `FW_JUMP=y` in platform `config.mk`
1. Spedifying `FW_JUMP=y` on the top level `make` command line.
2. Specifying `FW_JUMP=y` in the target platform *config.mk* configuration file.
Config Options
--------------
The compiled *FW_JUMP* firmware ELF file is named *fw_jump.elf*. Its expanded
image file is *fw_jump.bin*. Both files are created in the platform specific
build directory under the *build/platform/<platform_subdir>/firmware* directory.
We need more config details for **FW_JUMP** firmware to work
correctly. These configuration details can be passed as parameters to
top-level `make` or can be set in platform `config.mk`.
*FW_JUMP* Firmware Configuration Options
----------------------------------------
Following are the configuration options for a **FW_JUMP** firmware:
To operate correctly, a *FW_JUMP* firmware requires some configuration
parameters to be defined using either the top level `make` command line or the
target platform *config.mk* configuration file. The possible parameters are as
follows.
* **FW_JUMP_ADDR** - Address where next booting stage is
located. This is a mandatory config option and will result
in compile error if not provided.
* **FW_JUMP_ADDR** - Address of the entry point of the booting stage to be
executed following OpenSBI firmware. This address generally correspond
exactly to the address where this next booting stage was loaded. This is a
mandatory parameter. Compilation errors will result from not defining this
address.
* **FW_JUMP_FDT_ADDR** - Address where the FDT passed by the prior
booting stage will be placed before passing to the next booting
stage. If this option is not provided then the firmware will pass
zero as the FDT address to the next booting stage.
>>>>>>> 2c0dc4dc... docs: Typo fixes.
* **FW_JUMP_FDT_ADDR** - Address where the *flattened device tree (FDT file)*
passed by the prior booting stage will be placed in memory before executing
the booting stage following OpenSBI firmware. If this option is not provided
then OpenSBI firmware will pass zero as the FDT address to the following
booting stage.
*FW_JUMP* Example
-----------------
The *[qemu/virt]* and *[qemu/sifive_u]* platforms illustrates how to configure
and use a *FW_JUMP* firmware. Detailed information regarding these platforms
can be found in the platforms documentation files.
[qemu/virt]: ../platform/qemu_virt.md
[qemu/sifive_u]: ../platform/qemu_sifive_u.md