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opensbi/docs/blob/fw_payload.md
Anup Patel 33ec85c9ab docs: Add documentation for firmware blobs 
This patch adds documentation for fw_jump and fw_payload
firmware blobs.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
2018-12-21 07:28:33 +05:30

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OpenSBI Firmware with Payload (FW_PAYLOAD)

The OpenSBI firmware with Payload (FW_PAYLOAD) is a firmware which includes next booting stage binary (i.e. bootloader/kernel) as payload in the OpenSBI firmware binary.

This FW_PAYLOAD firmware is particularly useful when booting stage prior to OpenSBI firmware is not capable of loading OpenSBI firmware and booting stage after OpenSBI firmware separately.

It is also possible that booting stage prior to OpenSBI firmware does not pass flattened device tree (FDT). In this case, we have provision to embed FDT in .text section of FW_PAYLOAD firmware.

How to Enable?

The FW_PAYLOAD firmware can be enabled by any of the following methods:

  1. Passing FW_PAYLOAD=y command-line parameter to top-level make
  2. Setting FW_PAYLOAD=y in platform config.mk

Config Options

We need more config details for FW_PAYLOAD firmware to work correctly. These config details can be passed as paramter to top-level make or can be set in platform config.mk.

Following are the config options for FW_PAYLOAD firmware:

  • FW_PAYLOAD_OFFSET - Offset from FW_TEXT_BASE where next booting stage binary will be linked to FW_PAYLOAD firmware. This is a mandatory config option and will result in compile error if not provided.
  • FW_PAYLOAD_PATH - Path to the next booting stage binary. If this option is not provided then while (1) is taken as payload.
  • FW_PAYLOAD_FDT_PATH - Path to the FDT binary to be embedded in .text section of FW_PAYLOAD firmware. If this option is not provided then firmware will expect FDT to be passed by prior booting stage.
  • FW_PAYLOAD_FDT_ADDR - Address where FDT passed by prior booting stage (or embedded FDT) will be placed before passing to next booting stage. If this option is not provided then firmware will pass zero as FDT address to next booting stage.