[PATCH v5] user/exe: Add Device Tree section
Christian Mauderer
list at c-mauderer.de
Wed Aug 7 18:53:21 UTC 2019
The last changes from Gedare are integrated and the patch builds fine.
So I pushed it. Thanks for the work.
I'll wait with the libbsd patches till weekend so that someone could
still add an opinion (besides Chris and me).
Best regards
Christian
On 07/08/2019 18:02, Vijay Kumar Banerjee wrote:
> Ping :)
>
> On Sun, Aug 4, 2019 at 2:01 AM Vijay Kumar Banerjee
> <vijaykumar9597 at gmail.com <mailto:vijaykumar9597 at gmail.com>> wrote:
>
> ---
> user/bsps/arm/beagle.rst | 21 +--------
> user/exe/device-tree.rst | 92 ++++++++++++++++++++++++++++++++++++++++
> user/exe/index.rst | 1 +
> 3 files changed, 95 insertions(+), 19 deletions(-)
> create mode 100644 user/exe/device-tree.rst
>
> diff --git a/user/bsps/arm/beagle.rst b/user/bsps/arm/beagle.rst
> index eb4ecfb..fa7fa05 100644
> --- a/user/bsps/arm/beagle.rst
> +++ b/user/bsps/arm/beagle.rst
> @@ -40,25 +40,8 @@ from the libbsd HEAD of freebsd-org. For example
> if the HEAD is at
> Then the right Device Tree Source (DTS) file is:
> https://github.com/freebsd/freebsd/blob/19a6ceb89dbacf74697d493e48c388767126d418/sys/gnu/dts/arm/am335x-boneblack.dts
>
> -.. code-block:: shell
> - :linenos:
> -
> - #building the dtb
> - #We will use the script from
> https://github.com/freebsd/freebsd/blob/19a6ceb89dbacf74697d493e48c388767126d418/sys/tools/fdt/make_dtb.sh
> -
> - #The make_dtb.sh script uses environment variable MACHINE
> - export MACHINE='arm'
> -
> - SCRIPT_DIR=$HOME/freebsd/sys/tools/fdt
> -
> - #The arguments to the script are
> - # $1 -> Build Tree
> - # $2 -> DTS source file
> - # $3 -> output path of the DTB file
> -
> - ${SCRIPT_DIR}/make_dtb.sh ${SCRIPT_DIR}/../../ \
> - ${SCRIPT_DIR}/../../gnu/dts/arm/am335x-boneblack.dts \
> - $(pwd)
> +Please refer to the :ref:`device-tree` to know more about building
> and applying
> +the Device Trees.
>
> Writing the uEnv.txt file
> -------------------------
> diff --git a/user/exe/device-tree.rst b/user/exe/device-tree.rst
> new file mode 100644
> index 0000000..bd21552
> --- /dev/null
> +++ b/user/exe/device-tree.rst
> @@ -0,0 +1,92 @@
> +.. SPDX-License-Identifier: CC-BY-SA-4.0
> +
> +.. Copyright (C) 2019 Vijay Kumar Banerjee
> <vijaykumar9597 at gmail.com <mailto:vijaykumar9597 at gmail.com>>
> +
> +Device Tree
> +===========
> +.. index:: Device Tree
> +
> +A Device Tree is a data structure that is used to describe
> properties of
> +non-discoverable hardware instead of hardcoding them in the kernel.
> The device
> +tree data is generally stored in a `.dts` or a Device Tree Source
> (DTS) file.
> +This file is then compiled into a binary format called Device Tree
> Blob (DTB)
> +with `.dtb` extension. RTEMS preferably uses a DTB built from the
> FreeBSD source
> +tree matching the freebsd-org HEAD commit hash in libBSD.
> +
> +Building the DTB
> +----------------
> +
> +A single DTB file can be built using the `dtc` tool in libfdt using the
> +following command:
> +
> +.. code-block:: none
> +
> + dtc -@ -I dts -O dtb -o my-devicetree.dtb my-devicetree.dts
> +
> +For building the DTB from the FreeBSD source, the `make_dtb.sh` script
> +from `freebsd/sys/tools/fdt` must be used as most of the DTS files
> in FreeBSD
> +have included `.dtsi` files from their source tree. An example is
> given below as
> +a reference for how to build the device tree from the FreeBSD source.
> +
> +`NOTE: The following example uses FreeBSD master branch from github
> mirror as
> +an example. It is advised to always use the source from the commit
> matching the
> +freebsd-org HEAD in libBSD.`
> +
> +.. code-block:: shell
> + :linenos:
> +
> + #We're using the script from freebsd/sys/tools/make_dtb.sh
> + #Target device: Beaglebone Black.
> + #Architecture: Arm.
> + #DTS source name: am335x-boneblack.dts
> +
> + #The make_dtb.sh script uses environment variable MACHINE
> + export MACHINE='arm'
> +
> + SCRIPT_DIR=$HOME/freebsd/sys/tools/fdt
> +
> + #The arguments to the script are
> + # $1 -> Build Tree (This is the path to freebsd/sys/ directory)
> + # $2 -> DTS source file
> + # $3 -> output path of the DTB file
> +
> + ${SCRIPT_DIR}/make_dtb.sh ${SCRIPT_DIR}/../../ \
> + ${SCRIPT_DIR}/../../gnu/dts/arm/am335x-boneblack.dts \
> + $(pwd)
> +
> +Using Device Tree Overlay
> +-------------------------
> +
> +Device tree overlay is used either to add properties or devices to
> the existing
> +device tree. Adding any property to DTS using an overlay will
> override the
> +current values in the DTB. The Overlays enable us to modify the
> device tree
> +using a small maintainable plugin without having to edit the whole
> Base Tree.
> +
> +There are two ways of applying an overlay on top of the built DTB.
> +
> +#. Use fdtoverlay from libfdt
> +
> +#. Add the overlay in the root partition of the SD card and apply
> it using U-Boot
> +
> +The fdtoverlay command can be used as follows:
> +
> +.. code-block:: none
> +
> + fdtoverlay -i my-base-tree.dtb -o output-tree.dtb my-overlay.dtbo
> +
> +To apply it from U-Boot during system initialization we have to add
> the device
> +tree overlay file in the root directory of the SD card and use
> U-Boot commands
> +to apply the overlay.
> +
> +Below is given the series of U-Boot commands that can be used to
> apply the
> +overlay, given that the overlay blob (.dtbo) file is already in the
> card.
> +
> +.. code-block:: shell
> +
> + fatload mmc 0:1 0x80800000 rtems-app.img
> + fatload mmc 0:1 0x88000000 my-base-tree.dtb
> + fdt addr 0x88000000
> + fatload mmc 0:1 0x88100000 my-overlay.dtbo
> + fdt resize 0x1000
> + fdt apply 0x88100000
> + bootm 0x80800000-0x88000000
> diff --git a/user/exe/index.rst b/user/exe/index.rst
> index 3e9b571..e22420a 100644
> --- a/user/exe/index.rst
> +++ b/user/exe/index.rst
> @@ -21,3 +21,4 @@ execiutable, and creating and dynamically loading
> code.
> initialization
> debugging
> loader
> + device-tree
> --
> 2.20.1
>
>
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