Documentation: Various tweaks to user manual, device tree chapter.
Grammar, typoes, font, link fixes. Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
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@ -4,29 +4,29 @@ Devicetree support
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==================
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==================
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Flattened Device Tree (FDT) is a data structure for describing the hardware on
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Flattened Device Tree (FDT) is a data structure for describing the hardware on
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a system. On an increasing number of boards both barebox and the Linux Kernel can
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a system. On an increasing number of boards, both barebox and the Linux kernel can
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probe their devices directly from devicetrees. barebox needs the devicetree compiled
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probe their devices directly from devicetrees. barebox needs the devicetree compiled
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into the binary. The Kernel usually does not have a devicetree compiled in, instead
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into the binary. The kernel usually does not have a devicetree compiled in; instead,
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the Kernel expects to be passed a devicetree from the bootloader.
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the kernel expects to be passed a devicetree from the bootloader.
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From a bootloader's point of view, using devicetrees has the advantage that the
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From a bootloader's point of view, using devicetrees has the advantage that the
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same devicetree is used to probe both the Kernel and the Bootloader; this
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same devicetree can be used by both the bootloader and the kernel; this
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drastically reduces porting effort since the devicetree has to be written only
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drastically reduces porting effort since the devicetree has to be written only
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once (and with luck somebody has already written a devicetree for the Kernel).
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once (and with luck somebody has already written a devicetree for the kernel).
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Probing barebox from devicetree is highly recommended for new projects.
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Having barebox consult a devicetree is highly recommended for new projects.
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.. _internal_devicetree:
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.. _internal_devicetree:
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The internal devicetree
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The internal devicetree
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-----------------------
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-----------------------
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The devicetree barebox has been probed from plays a special role. It is referred to
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The devicetree consulted by barebox plays a special role. It is referred to
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as the :ref:`internal_devicetree`. The barebox devicetree commands work on this
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as the "internal devicetree." The barebox devicetree commands work on this
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devicetree. The devicetree source (DTS) files are kept in sync with the Kernel DTS
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devicetree. The devicetree source (DTS) files are kept in sync with the kernel DTS
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files. As the FDT files are meant to be backward compatible, it should always be possible
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files. As the FDT files are meant to be backward compatible, it should always be possible
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to start a Kernel with the barebox internal devicetree. However, since the barebox
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to start a kernel with the barebox internal devicetree. However, since the barebox
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devicetree may not be complete or contain bugs it is always possible to start the
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devicetree may not be complete or contain bugs it is always possible to start the
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Kernel with another devicetree than barebox has been started with.
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kernel with a devicetree different from the one used by barebox.
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If a device has been probed from the devicetree then using the :ref:`command_devinfo`
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If a device has been probed from the devicetree then using the :ref:`command_devinfo`
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command on it will show the corresponding devicetree node:
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command on it will show the corresponding devicetree node:
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@ -73,10 +73,11 @@ work on the internal devicetree. It is possible to add/remove nodes using the
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It is important to know that these commands always work on the internal
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It is important to know that these commands always work on the internal
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devicetree. If you modify the internal devicetree to influence the behaviour of
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devicetree. If you modify the internal devicetree to influence the behaviour of
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a Kernel booted later, make sure that you start the kernel with the internal
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a kernel booted later, make sure that you start the kernel with the internal
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devicetree (i.e. don't pass a devicetree to the :ref:`command_bootm` command). If you
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devicetree (i.e. don't pass a devicetree to the :ref:`command_bootm` command). If you
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wish to use another devicetree than the internal devicetree for starting the Kernel,
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wish to use another devicetree than the internal devicetree for starting the kernel,
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you can exchange the internal devicetree during runtime:
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you can exchange the internal devicetree during runtime using the
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:ref:`command_oftree` command:
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.. code-block:: sh
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.. code-block:: sh
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