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opensbi/docs/firmware/fw_payload.md
Damien Le Moal 0df8269477 Makefile: Add support for device tree compilation 
Add rules to compile dts files into dtb files using the device tree
compiler (dtc). A platform can specify the DTS file to compile using
the platform-dtb-y variable. The flattened device tree binary file to be
used for building the final polatform firmware can be specified using
the new FW_PAYLOAD_FDT firmware configuration option to point to the
automatically compiled FDT file. Using the existing FW_PAYLOAD_FDT_PATH
configuration option is still possible and will take precedence over
the FW_PAYLOAD_FDT definition.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
2019-01-21 09:58:33 +05:30

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OpenSBI Firmware with Payload (FW_PAYLOAD)

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

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

It is also possible that the booting stage prior to OpenSBI firmware does not pass a flattened device tree (FDT). In this case, a FW_PAYLOAD firmware allows embedding a flattened device tree in the .text section of the final 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

Configuration Options

A FW_PAYLOAD firmware needs to be built according to some predefined configuation options to work correctly. These configuration details can be passed as paramters to the top-level make command or can be defined in a platform config.mk build configuration file.

The following are the build configuration parameters for a FW_PAYLOAD firmware:

  • FW_PAYLOAD_OFFSET - Offset from FW_TEXT_BASE where the payload binary will be linked in the final FW_PAYLOAD firmware binary image. This configuration parameter is mandatory if FW_PAYLOAD_ALIGN is not defined. Compilation errors will result from an incorrect definition of FW_PAYLOAD_OFFSET or FW_PAYLOAD_ALIGN, or if neither of these paramreters are defined.

  • FW_PAYLOAD_ALIGN - Address alignment constraint where the payload binary will be linked after the end of the base firmaware binary in the final FW_PAYLOAD firmware binary image. This configuration parameter is mandatory if FW_PAYLOAD_OFFSET is not defined and should not be defined otherwise.

  • FW_PAYLOAD_PATH - Path to the next booting stage binary image file. If this option is not provided then a simple test payload is automatically generated, executing a while (1) loop.

  • FW_PAYLOAD_FDT_PATH - Path to an external flattened device tree binary file to be embedded in the .text section of the final FW_PAYLOAD firmware. If this option is not provided and no internal device tree file is specified by the platform (c.f. FW_PAYLOAD_FDT), then the firmware will expect the FDT to be passed as an argument by the prior booting stage.

  • FW_PAYLOAD_FDT - Path to an internal flattened device tree binary file defined by the platform code. The file name must match the DTB file name specified in the platform objects.mk file with the platform-dtb-y entry. This option results in FW_PAYLOAD_FDT_PATH to be automatically set. Specifying FW_PAYLOAD_FDT_PATH on the make command line disables FW_PAYLOAD_FDT and the command line specified device tree binary file is used for building the final firmware.

  • FW_PAYLOAD_FDT_ADDR - Address where the FDT passed by the prior booting stage or specified by the FW_PAYLOAD_FDT_PATH parameter and embedded in the .text section will be placed before executing the next booting stage, that is, the payload firmware. If this option is not provided then the firmware will pass zero as the FDT address to the next booting stage.