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This question comes up every now and then with people coming from Linux. Add some notes about it so we can point to it in the mailing list. Signed-off-by: Simon Glass <sjg@chromium.org> Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
45 lines
1.7 KiB
ReStructuredText
45 lines
1.7 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+
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Devicetree Introduction
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=======================
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U-Boot uses a devicetree for configuration. This includes the devices used by
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the board, the format of the image created with binman, which UART to use for
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the console, public keys used for secure boot and many other things.
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See :doc:`control` for more information.
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Why does U-Boot put <thing> in the devicetree?
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----------------------------------------------
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This question comes up a lot with people new to U-Boot, particular those coming
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from Linux who are used to quite strict rules about what can go into the
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devicetree.
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U-Boot uses the same devicetree as Linux but adds more things necessary for the
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bootloader environment (see :ref:`dttweaks`).
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U-Boot does not have a user space to provide policy and configuration. It cannot
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do what Linux does and run programs and look up filesystems to figure out how to
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boot. So configuration and runtime information goes into the devicetree in
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U-Boot.
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Of course it is possible to:
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- add tables into the rodata section of the U-Boot binary
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- append some info to the end of U-Boot in a different format
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- modify the linker script to bring in a file with some info in it
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- put things in ACPI tables
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- link in a UEFI hand-off block structure and put things in there
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but *please don't*. In general, devicetree is the sane place to hold U-Boot's
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configuration.
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So, please, do NOT ask why U-Boot puts <thing> in the devicetree. It is the only
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place it can go. It is a highly suitable data structure for just about anything
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that U-Boot needs to know at runtime.
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Note, it is possible to use platdata directly so drivers avoid devicetreee in
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SPL. But of-platdata is the modern way of avoiding devicetree overhead, so
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please use that instead.
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