+# SPDX-License-Identifier: GPL-2.0+
#
# Copyright (c) 2011 The Chromium OS Authors.
-#
-# See file CREDITS for list of people who contributed to this
-# project.
-#
-# This program is free software; you can redistribute it and/or
-# modify it under the terms of the GNU General Public License as
-# published by the Free Software Foundatio; either version 2 of
-# the License, or (at your option) any later version.
-#
-# This program is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-# GNU General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License
-# along with this program; if not, write to the Free Software
-# Foundation, Inc., 59 Temple Place, Suite 330, Boston,
-# MA 02111-1307 USA
-#
Device Tree Control in U-Boot
=============================
Tools
-----
-To use this feature you will need to get the device tree compiler here:
+To use this feature you will need to get the device tree compiler. This is
+provided by U-Boot automatically. If you have a system version of dtc
+(typically in the 'device-tree-compiler' package), it is currently not used.
- git://jdl.com/software/dtc.git
+If you want to build your own dtc, it is kept here:
+
+ git://git.kernel.org/pub/scm/utils/dtc/dtc.git
For example:
- $ git clone git://jdl.com/software/dtc.git
+ $ git clone git://git.kernel.org/pub/scm/utils/dtc/dtc.git
$ cd dtc
$ make
$ sudo make install
* Bad configuration: 0
* Strange test result: 0
-You will also find a useful ftdump utility for decoding a binary file.
+You will also find a useful fdtdump utility for decoding a binary file, as
+well as fdtget/fdtput for reading and writing properties in a binary file.
Where do I get an fdt file for my board?
board/<vendor>/dts/<name>.dts
This should include your CPU or SOC's device tree file, placed in
-arch/<arch>/dts, and then make any adjustments required. The name of this
-is CONFIG_ARCH_DEVICE_TREE.dts.
+arch/<arch>/dts, and then make any adjustments required.
If CONFIG_OF_EMBED is defined, then it will be picked up and built into
-the U-Boot image (including u-boot.bin).
+the U-Boot image (including u-boot.bin). This is suitable for debugging
+and development only and is not recommended for production devices.
If CONFIG_OF_SEPARATE is defined, then it will be built and placed in
-a u-boot.dtb file alongside u-boot.bin. A common approach is then to
+a u-boot.dtb file alongside u-boot-nodtb.bin. A common approach is then to
join the two:
- cat u-boot.bin u-boot.dtb >image.bin
+ cat u-boot-nodtb.bin u-boot.dtb >image.bin
+
+and then flash image.bin onto your board. Note that U-Boot creates
+u-boot-dtb.bin which does the above step for you also. Resulting
+u-boot.bin is a copy of u-boot-dtb.bin in this case. If you are using
+CONFIG_SPL_FRAMEWORK, then u-boot.img will be built to include the device
+tree binary.
-and then flash image.bin onto your board.
+If CONFIG_OF_BOARD is defined, a board-specific routine will provide the
+device tree at runtime, for example if an earlier bootloader stage creates
+it and passes it to U-Boot.
If CONFIG_OF_HOSTFILE is defined, then it will be read from a file on
startup. This is only useful for sandbox. Use the -d flag to U-Boot to
You cannot use more than one of these options at the same time.
+To use a device tree file that you have compiled yourself, pass
+EXT_DTB=<filename> to 'make', as in:
+
+ make EXT_DTB=boot/am335x-boneblack-pubkey.dtb
+
+Then U-Boot will copy that file to u-boot.dtb, put it in the .img file
+if used, and u-boot-dtb.bin.
+
If you wish to put the fdt at a different address in memory, you can
define the "fdtcontroladdr" environment variable. This is the hex
address of the fdt binary blob, and will override either of the options.
Be aware that this environment variable is checked prior to relocation,
when only the compiled-in environment is available. Therefore it is not
possible to define this variable in the saved SPI/NAND flash
-environment, for example (it will be ignored).
+environment, for example (it will be ignored). After relocation, this
+variable will be set to the address of the newly relocated fdt blob.
+It is read-only and cannot be changed. It can optionally be used to
+control the boot process of Linux with bootm/bootz commands.
To use this, put something like this in your board header file:
$ make DEVICE_TREE=<dts-file-name>
+Relocation, SPL and TPL
+-----------------------
+
+U-Boot can be divided into three phases: TPL, SPL and U-Boot proper.
+
+The full device tree is available to U-Boot proper, but normally only a subset
+(or none at all) is available to TPL and SPL. See 'Pre-Relocation Support' and
+'SPL Support' in doc/driver-model/design.rst for more details.
+
+
+Using several DTBs in the SPL (CONFIG_SPL_MULTI_DTB)
+----------------------------------------------------
+In some rare cases it is desirable to let SPL be able to select one DTB among
+many. This usually not very useful as the DTB for the SPL is small and usually
+fits several platforms. However the DTB sometimes include information that do
+work on several platforms (like IO tuning parameters).
+In this case it is possible to use CONFIG_SPL_MULTI_DTB. This option appends to
+the SPL a FIT image containing several DTBs listed in SPL_OF_LIST.
+board_fit_config_name_match() is called to select the right DTB.
+
+If board_fit_config_name_match() relies on DM (DM driver to access an EEPROM
+containing the board ID for example), it possible to start with a generic DTB
+and then switch over to the right DTB after the detection. For this purpose,
+the platform code must call fdtdec_resetup(). Based on the returned flag, the
+platform may have to re-initiliaze the DM subusystem using dm_uninit() and
+dm_init_and_scan().
+
+
Limitations
-----------
projects / oweals / u-boot.git / blobdiff