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docs: Document parameters passed to firmware and alignment requirement
This updates documentation to describe parameters passed to firmware from previous booting stage, and corresponding address alignment requirement. This also fixes a typo in fw_dynamic.md (it's => its). Signed-off-by: Bin Meng <bmeng.cn@gmail.com> Reviewed-by: Anup Patel <anup.patel@wdc.com>
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@@ -9,6 +9,13 @@ 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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The previous booting stage will pass information via the following registers
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of RISC-V CPU:
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* hartid via *a0* register
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* device tree blob address in memory via *a1* register. The address must
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be aligned to 8 bytes.
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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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@@ -6,8 +6,9 @@ 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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*struct fw_dynamic_info* in memory and passing its address to *FW_DYNAMIC*
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via *a2* register of RISC-V CPU. The address must be aligned to 8 bytes on
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RV64 and 4 bytes on RV32.
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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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