106 lines
4.3 KiB
Markdown
106 lines
4.3 KiB
Markdown
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OpenSBI Platform Firmwares
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==========================
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OpenSBI provides firmware builds for specific platforms. Different types of
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firmwares are supported to deal with the differences between different platforms
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early boot stage. All firmwares will execute the same initialization procedure
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of the platform hardware according to the platform specific code as well as
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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 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 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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A *FW_JUMP* 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 Payload (*FW_PAYLOAD*)
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------------------------------------
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The *FW_PAYLOAD* firmware directly includes the binary code for the booting
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stage to follow OpenSBI firmware execution. Typically, this payload will be a
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bootloader or an OS kernel.
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A *FW_PAYLOAD* firmware is particularly useful when the booting stage executed
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prior to OpenSBI firmware is not capable of loading both OpenSBI firmware and
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the booting stage to follow OpenSBI firmware.
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A *FW_PAYLOAD* firmware is also useful for cases where the booting stage prior
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to OpenSBI firmware does not pass a *flattened device tree (FDT file)*. In such
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case, a *FW_PAYLOAD* firmware allows embedding a flattened device tree in the
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.text section of the final firmware.
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Firmware Configuration and Compilation
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--------------------------------------
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All firmware types mandate the definition of the following compile time
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configuration parameter.
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* **FW_TEXT_ADDR** - Defines the address at which the previous booting stage
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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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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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Providing different payloads to OpenSBI Firmware
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------------------------------------------------
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OpenSBI firmware can accept various payloads using a compile time option.
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Typically, these payloads refer to the next stage boot loader (e.g. U-Boot)
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or operating system kernel images (e.g. Linux). By default, OpenSBI
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automatically provides a test payload if no specific payload is specified
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at compile time.
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To specify a payload at compile time, the make variable _FW_PAYLOAD_PATH_ is
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used.
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```
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make PLATFORM=<platform_subdir> FW_PAYLOAD_PATH=<payload path>
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```
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The instructions to build each payload is different and the details can
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be found in the
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*docs/firmware/payload_<payload_name>.md* files.
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Options for OpenSBI Firmware behaviors
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--------------------------------------
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An optional compile time flag FW_OPTIONS can be used to control the OpenSBI
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firmware run-time behaviors.
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```
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make PLATFORM=<platform_subdir> FW_OPTIONS=<options>
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```
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FW_OPTIONS is a bitwise or'ed value of various options, eg: *FW_OPTIONS=0x1*
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stands for disabling boot prints from the OpenSBI library.
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For all supported options, please check "enum sbi_scratch_options" in the
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*include/sbi/sbi_scratch.h* header file.
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