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doc: dts: clarify a design requirement

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There's been some confusion about what we mean by hardware
description. We're really talking about the user-facing inputs that
need to be configured per SoC, application, etc. It's fine to do
things like use ifdeffery on a CMSIS header in an aarch32 support file
to decide if the current target has some feature, for instance -- that
sort of thing doesn't *have* to come from DT.

At the same time, we don't want to encourage vendor-specific hardware
configuration languages from creeping into upstream zephyr, so keep
the language strong in an effort to avoid that misinterpretation.

Signed-off-by: Marti Bolivar <marti.bolivar@nordicsemi.no>
This commit is contained in:
Marti Bolivar 2023-01-11 14:30:33 -08:00
commit 67b0cd382e
1 changed files with 8 additions and 6 deletions
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14
doc/build/dts/design.rst vendored
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@ -8,23 +8,25 @@ changes are expected. The following are the general design goals, along with
specific examples about how they impact Zephyr's source code, and areas where specific examples about how they impact Zephyr's source code, and areas where
more work remains to be done. more work remains to be done.
Single source for all hardware information Single source for hardware information
****************************************** **************************************
Zephyr shall obtain its hardware descriptions exclusively from devicetree. Zephyr's built-in device drivers and sample applications shall obtain
configurable hardware descriptions from devicetree.
Examples Examples
======== ========
- New device drivers shall use devicetree APIs to determine which :ref:`devices - New device drivers shall use devicetree APIs to determine which :ref:`devices
to create <dt-create-devices>` if possible. to create <dt-create-devices>`.
- In-tree sample applications shall use :ref:`aliases <dt-alias-chosen>` to - In-tree sample applications shall use :ref:`aliases <dt-alias-chosen>` to
determine which of multiple possible generic devices of a given type will be determine which of multiple possible generic devices of a given type will be
used in the current build. For example, the :ref:`blinky-sample` uses this to used in the current build. For example, the :ref:`blinky-sample` uses this to
determine the LED to blink. determine the LED to blink.
- Boot-time pin muxing and pin control can be accomplished via devicetree. - Boot-time pin muxing and pin control for new SoCs shall be accomplished via a
devicetree-based pinctrl driver
Example remaining work Example remaining work
====================== ======================
@ -33,7 +35,7 @@ Example remaining work
determine the hardware supported by a board. This should be obtained from determine the hardware supported by a board. This should be obtained from
devicetree instead. devicetree instead.
- Various device drivers currently use Kconfig to determine which instances of a - Legacy device drivers currently use Kconfig to determine which instances of a
particular compatible are enabled. This can and should be done with devicetree particular compatible are enabled. This can and should be done with devicetree
overlays instead. overlays instead.