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Add some documentation to explain the basic concept along with a link to the full spec. Signed-off-by: Simon Glass <sjg@chromium.org>
46 lines
1.4 KiB
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46 lines
1.4 KiB
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.. SPDX-License-Identifier: GPL-2.0-or-later
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Universal Payload
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-----------------
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`Universal Payload (UPL) <https://universalpayload.github.io/spec/index.html>`_
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is an Industry Standard for firmware components. UPL
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is designed to improve interoperability within the firmware industry, allowing
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mixing and matching of projects with less friction and fewer project-specific
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implementations. UPL is cross-platform, supporting ARM, x86 and RISC-V
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initially.
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UPL is defined in termns of two firmware components:
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`Platform Init`
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Perhaps initial setup of the hardware and jumps to the payload.
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`Payload`
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Selects the OS to boot
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In practice UPL can be used to handle any number of handoffs through the
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firmware startup process, with one program acting as platform init and another
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acting as the payload.
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UPL provides a standard for three main pieces:
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- file format for the payload, which may comprise multiple images to load
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- handoff format for the information the payload needs, such as serial port,
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memory layout, etc.
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- machine state and register settings at the point of handoff
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See also the :doc:`cmd/upl`.
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UPL in U-Boot
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~~~~~~~~~~~~~
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U-Boot supports:
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- writing a UPL handoff (devicetree) in SPL
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- reading a UPL handoff in U-Boot proper
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- creating a FIT
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There are some new FIT features in UPL which are not yet supported in U-Boot.
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.. sectionauthor:: Simon Glass <sjg@chromium.org>
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.. July 2024
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