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docs: Add documentation about dynamic firmware
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>
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2 changed files with 51 additions and 3 deletions
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@ -9,12 +9,22 @@ OpenSBI generic library code. The supported firmwares type will differ in how
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the arguments passed by the platform early boot stage are handled, as well as
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how the boot stage following the firmware will be handled and executed.
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OpenSBI currently supports two different types of firmwares.
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OpenSBI currently supports three different types of firmwares.
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Firmware with Dynamic Information (*FW_DYNAMIC*)
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------------------------------------------------
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The *FW_DYNAMIC* firmware gets information about the next booting stage entry,
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e.g. a bootloader or an OS kernel, from previous booting stage at runtime.
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A *FW_DYNAMIC* firmware is particularly useful when the booting stage executed
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prior to OpenSBI firmware is capable of loading both the OpenSBI firmware
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and the booting stage binary to follow OpenSBI firmware.
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Firmware with Jump Address (*FW_JUMP*)
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--------------------------------------
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The *FW_JUMP* firmware only handles the address of the next booting stage
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The *FW_JUMP* firmware assumes a fixed address of the next booting stage
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entry, e.g. a bootloader or an OS kernel, without directly including the
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binary code for this next stage.
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@ -48,14 +58,17 @@ configuration parameter.
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loads OpenSBI firmware.
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Additionally, each firmware type as a set of type specific configuration
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parameters. Detailed information for each firmware type can be found in the
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parameters. Detailed information for each firmware type can be found in the
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following documents.
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* *[FW_DYNAMIC]*: The *Firmware with Dynamic Information (FW_DYNAMIC)* is
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described in more details in the file *fw_dynamic.md*.
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* *[FW_JUMP]*: The *Firmware with Jump Address (FW_JUMP)* is described in more
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details in the file *fw_jump.md*.
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* *[FW_PAYLOAD]*: The *Firmware with Payload (FW_PAYLOAD)* is described in more
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details in the file *fw_payload.md*.
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[FW_DYNAMIC]: fw_dynamic.md
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[FW_JUMP]: fw_jump.md
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[FW_PAYLOAD]: fw_payload.md
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35
docs/firmware/fw_dynamic.md
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35
docs/firmware/fw_dynamic.md
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OpenSBI Firmware with Dynamic Information *FW_DYNAMIC*
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======================================================
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OpenSBI **firmware with dynamic info (FW_DYNAMIC)** is a firmware which gets
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information about next booting stage (e.g. a bootloader or an OS) and runtime
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OpenSBI library options from previous booting stage.
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The previous booting stage will pass information to *FW_DYNAMIC* by creating
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*struct fw_dynamic_info* in memory and passing it's address to *FW_DYNAMIC*
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via *a2* register of RISC-V CPU.
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A *FW_DYNAMIC* firmware is particularly useful when the booting stage executed
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prior to OpenSBI firmware is capable of loading both the OpenSBI firmware and
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the booting stage binary to follow OpenSBI firmware.
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*FW_DYNAMIC* Compilation
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------------------------
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A platform can enable *FW_DYNAMIC* firmware using any of the following methods.
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1. Specifying `FW_DYNAMIC=y` on the top level `make` command line.
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2. Specifying `FW_DYNAMIC=y` in the target platform *config.mk* configuration
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file.
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The compiled *FW_DYNAMIC* firmware ELF file is named *fw_dynamic.elf*. It's
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expanded image file is *fw_dynamic.bin*. Both files are created in the platform
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specific build directory under the *build/platform/<platform_subdir>/firmware*
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directory.
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*FW_DYNAMIC* Firmware Configuration Options
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-------------------------------------------
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The *FW_DYNAMIC* firmware does not requires any platform specific configuration
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parameters because all required information is passed by previous booting stage
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at runtime via *struct fw_dynamic_info*.
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