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doc: dts: Explain better how devicetree and Kconfig fit together

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It's cryptic that some identifiers for devicetree-related stuff start
with DT_*, while others start with CONFIG_*. Explain what's going on,
and link to the Kconfig preprocessor documentation.

Also remove an early mention of bindings that might be confusing.
Bindings are much more about checking devicetree conformance than about
controlling output, though they do some of that too.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>
This commit is contained in:
Ulf Magnusson 2019-12-26 13:59:16 +01:00 • committed by Carles Cufí
commit 5b497cf7ce
1 changed files with 13 additions and 7 deletions
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20
doc/guides/dts/index.rst
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@ -23,12 +23,15 @@ This figure shows how devicetree fits into the Zephyr build system:
Devicetree build flow
Zephyr's build system can use a devicetree to generate C language code. This
code generation uses rules in additional files called :ref:`devicetree bindings
<bindings>` to control how devicetree data is converted to C definitions. The
generated code can be included by Zephyr :ref:`device drivers <device_drivers>`
and other C sources. The C macros generated by this process all begin with
``DT_``.
Zephyr's build system generates C preprocessor macros from devicetree
definitions. These macros can be referenced in :ref:`device drivers
<device_drivers>` and other C code. All macro identifiers that are directly
generated by the devicetree scripts start with ``DT_*``.
Some devicetree-related identifiers also start with ``CONFIG_*``, which is the
identifier prefix used by :ref:`Kconfig <kconfig>`. This happens when
devicetree-related information is referenced from Kconfig symbol definitions,
via the :ref:`Kconfig preprocessor <kconfig-functions>`.
This differs significantly from how devicetree is used on Linux. The
Linux kernel would instead read the entire devicetree data structure in its
@ -470,7 +473,10 @@ to ``uart1`` in this board:
zephyr,shell-uart = &uart1;
};
The full set of Zephyr-specific ``chosen`` nodes follows:
The table below lists Zephyr-specific ``chosen`` properties. The macro
identifiers that start with ``CONFIG_*`` are generated from Kconfig symbols
that reference devicetree data via the :ref:`Kconfig preprocessor
<kconfig-functions>`.
.. list-table::
:header-rows: 1