u-boot/doc/README.fdt-control

1 # SPDX-License-Identifier: GPL-2.0+
5 Device Tree Control in U-Boot
8 This feature provides for run-time configuration of U-Boot via a flat
9 device tree (fdt). U-Boot configuration has traditionally been done
11 make it possible for a single U-Boot binary to support multiple boards,
16 The fdt is a convenient vehicle for implementing run-time configuration
23 format, and a library is already available in U-Boot (libfdt) for
27 and embedding it in your U-Boot image. This is useful since it allows
28 U-Boot to configure itself according to what it finds there. If you have
30 the features of each board in the device tree file, and have a single
37 ---------------------------
47 	Documentation/devicetree/booting-without-of.txt
51 	http://lists.ozlabs.org/listinfo/devicetree-discuss
57 -----
60 provided by U-Boot automatically. If you have a system version of dtc
61 (typically in the 'device-tree-compiler' package), it is currently not used.
63 If you want to build your own dtc, it is kept here:
76 	$ dtc -v
77 	Version: DTC 1.2.0-g2cb4b51f
93 ----------------------------------------
106 -------------
121 the U-Boot image (including u-boot.bin). This is suitable for debugging
125 a u-boot.dtb file alongside u-boot-nodtb.bin. A common approach is then to
128 	cat u-boot-nodtb.bin u-boot.dtb >image.bin
130 and then flash image.bin onto your board. Note that U-Boot creates
131 u-boot-dtb.bin which does the above step for you also. Resulting
132 u-boot.bin is a copy of u-boot-dtb.bin in this case. If you are using
133 CONFIG_SPL_FRAMEWORK, then u-boot.img will be built to include the device
136 If CONFIG_OF_BOARD is defined, a board-specific routine will provide the
138 it and passes it to U-Boot.
141 startup. This is only useful for sandbox. Use the -d flag to U-Boot to
149 	make EXT_DTB=boot/am335x-boneblack-pubkey.dtb
151 Then U-Boot will copy that file to u-boot.dtb, put it in the .img file
152 if used, and u-boot-dtb.bin.
158 when only the compiled-in environment is available. Therefore it is not
162 It is read-only and cannot be changed. It can optionally be used to
169 Build:
171 After board configuration is done, fdt supported u-boot can be build in two ways:
172 1)  build the default dts which is defined from CONFIG_DEFAULT_DEVICE_TREE
174 2)  build the user specified dts file
175     $ make DEVICE_TREE=<dts-file-name>
179 -----------------------
181 U-Boot can be divided into three phases: TPL, SPL and U-Boot proper.
183 The full device tree is available to U-Boot proper, but normally only a subset
184 (or none at all) is available to TPL and SPL. See 'Pre-Relocation Support' and
185 'SPL Support' in doc/driver-model/README.txt for more details.
189 ----------------------------------------------------
202 platform may have to re-initiliaze the DM subusystem using dm_uninit() and
207 -----------
209 U-Boot is designed to build with a single architecture type and CPU
210 type. So for example it is not possible to build a single ARM binary
212 the various features. This is because you must select one of
213 the CPU families within arch/arm/cpu/arm926ejs (omap or at91) at build
214 time. Similarly you cannot build for multiple cpu types or
228 --
230 1-Sep-11