--- /dev/null
+#
+# 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
+=============================
+
+This feature provides for run-time configuration of U-Boot via a flat
+device tree (fdt). U-Boot configuration has traditionally been done
+using CONFIG options in the board config file. This feature aims to
+make it possible for a single U-Boot binary to support multiple boards,
+with the exact configuration of each board controlled by a flat device
+tree (fdt). This is the approach recently taken by the ARM Linux kernel
+and has been used by PowerPC for some time.
+
+The fdt is a convenient vehicle for implementing run-time configuration
+for three reasons. Firstly it is easy to use, being a simple text file.
+It is extensible since it consists of nodes and properties in a nice
+hierarchical format.
+
+Finally, there is already excellent infrastructure for the fdt: a
+compiler checks the text file and converts it to a compact binary
+format, and a library is already available in U-Boot (libfdt) for
+handling this format.
+
+The dts directory contains a Makefile for building the device tree blob
+and embedding it in your U-Boot image. This is useful since it allows
+U-Boot to configure itself according to what it finds there. If you have
+a number of similar boards with different peripherals, you can describe
+the features of each board in the device tree file, and have a single
+generic source base.
+
+To enable this feature, add CONFIG_OF_CONTROL to your board config file.
+
+
+What is a Flat Device Tree?
+---------------------------
+
+An fdt can be specified in source format as a text file. To read about
+the fdt syntax, take a look at the specification here:
+
+https://www.power.org/resources/downloads/Power_ePAPR_APPROVED_v1.0.pdf
+
+You also might find this section of the Linux kernel documentation
+useful: (access this in the Linux kernel source code)
+
+ Documentation/devicetree/booting-without-of.txt
+
+There is also a mailing list:
+
+ http://lists.ozlabs.org/listinfo/devicetree-discuss
+
+In case you are wondering, OF stands for Open Firmware.
+
+
+Tools
+-----
+
+To use this feature you will need to get the device tree compiler here:
+
+ git://jdl.com/software/dtc.git
+
+For example:
+
+ $ git clone git://jdl.com/software/dtc.git
+ $ cd dtc
+ $ make
+ $ sudo make install
+
+Then run the compiler (your version will vary):
+
+ $ dtc -v
+ Version: DTC 1.2.0-g2cb4b51f
+ $ make tests
+ $ cd tests
+ $ ./run_tests.sh
+ ********** TEST SUMMARY
+ * Total testcases: 1371
+ * PASS: 1371
+ * FAIL: 0
+ * Bad configuration: 0
+ * Strange test result: 0
+
+You will also find a useful ftdump utility for decoding a binary file.
+
+
+Where do I get an fdt file for my board?
+----------------------------------------
+
+You may find that the Linux kernel has a suitable file. Look in the
+kernel source in arch/<arch>/boot/dts.
+
+If not you might find other boards with suitable files that you can
+modify to your needs. Look in the board directories for files with a
+.dts extension.
+
+Failing that, you could write one from scratch yourself!
+
+
+Configuration
+-------------
+
+Use:
+
+#define CONFIG_DEFAULT_DEVICE_TREE "<name>"
+
+to set the filename of the device tree source. Then put your device tree
+file into
+
+ 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.
+
+If CONFIG_OF_EMBED is defined, then it will be picked up and built into
+the U-Boot image (including u-boot.bin).
+
+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
+join the two:
+
+ cat u-boot.bin u-boot.dtb >image.bin
+
+and then flash image.bin onto your board.
+
+You cannot use both of these options at the same time.
+
+
+Limitations
+-----------
+
+U-Boot is designed to build with a single architecture type and CPU
+type. So for example it is not possible to build a single ARM binary
+which runs on your AT91 and OMAP boards, relying on an fdt to configure
+the various features. This is because you must select one of
+the CPU families within arch/arm/cpu/arm926ejs (omap or at91) at build
+time. Similarly you cannot build for multiple cpu types or
+architectures.
+
+That said the complexity reduction by using fdt to support variants of
+boards which use the same SOC / CPU can be substantial.
+
+It is important to understand that the fdt only selects options
+available in the platform / drivers. It cannot add new drivers (yet). So
+you must still have the CONFIG option to enable the driver. For example,
+you need to define CONFIG_SYS_NS16550 to bring in the NS16550 driver,
+but can use the fdt to specific the UART clock, peripheral address, etc.
+In very broad terms, the CONFIG options in general control *what* driver
+files are pulled in, and the fdt controls *how* those files work.
+
+--
+Simon Glass <sjg@chromium.org>
+1-Sep-11
--- /dev/null
+#
+# 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
+#
+
+# This Makefile builds the internal U-Boot fdt if CONFIG_OF_CONTROL is
+# enabled. See doc/README.fdt-control for more details.
+
+include $(TOPDIR)/config.mk
+
+LIB = $(obj)libdts.o
+
+$(if $(CONFIG_DEFAULT_DEVICE_TREE),,\
+$(error Please define CONFIG_DEFAULT_DEVICE_TREE in your board header file))
+DEVICE_TREE = $(subst ",,$(CONFIG_DEFAULT_DEVICE_TREE))
+
+$(if $(CONFIG_ARCH_DEVICE_TREE),,\
+$(error Your architecture does not have device tree support enabled. \
+Please define CONFIG_ARCH_DEVICE_TREE))
+
+# We preprocess the device tree file provide a useful define
+DTS_CPPFLAGS := -DARCH_CPU_DTS=\"../arch/$(ARCH)/dts/$(CONFIG_ARCH_DEVICE_TREE).dtsi\"
+
+all: $(obj).depend $(LIB)
+
+# Use a constant name for this so we can access it from C code.
+# objcopy doesn't seem to allow us to set the symbol name independently of
+# the filename.
+DT_BIN := $(obj)dt.dtb
+
+$(DT_BIN): $(TOPDIR)/board/$(VENDOR)/dts/$(DEVICE_TREE).dts
+ cat $< | $(CPP) -P $(DTS_CPPFLAGS) - >$@.tmp
+ $(DTC) -R 4 -p 0x1000 -O dtb -o ${DT_BIN} $@.tmp
+ rm $@.tmp
+
+process_lds = \
+ $(1) | sed -r -n 's/^OUTPUT_$(2)[ ("]*([^")]*).*/\1/p'
+
+# Run the compiler and get the link script from the linker
+GET_LDS = $(CC) $(CFLAGS) $(LDFLAGS) -Wl,--verbose 2>&1
+
+$(obj)dt.o: $(DT_BIN)
+ # We want the output format and arch.
+ # We also hope to win a prize for ugliest Makefile / shell interaction
+ # We look in the LDSCRIPT first.
+ # Then try the linker which should give us the answer.
+ # Then check it worked.
+ oformat=`$(call process_lds,cat $(LDSCRIPT),FORMAT)` ;\
+ oarch=`$(call process_lds,cat $(LDSCRIPT),ARCH)` ;\
+ \
+ [ -z $${oformat} ] && \
+ oformat=`$(call process_lds,$(GET_LDS),FORMAT)` ;\
+ [ -z $${oarch} ] && \
+ oarch=`$(call process_lds,$(GET_LDS),ARCH)` ;\
+ \
+ [ -z $${oformat} ] && \
+ echo "Cannot read OUTPUT_FORMAT from lds file $(LDSCRIPT)" && \
+ exit 1 || true ;\
+ [ -z $${oarch} ] && \
+ echo "Cannot read OUTPUT_ARCH from lds file $(LDSCRIPT)" && \
+ exit 1 || true ;\
+ \
+ cd $(dir ${DT_BIN}) && \
+ $(OBJCOPY) -I binary -O $${oformat} -B $${oarch} \
+ $(notdir ${DT_BIN}) $@
+ rm $(DT_BIN)
+
+OBJS-$(CONFIG_OF_EMBED) := dt.o
+
+COBJS := $(OBJS-y)
+
+OBJS := $(addprefix $(obj),$(COBJS))
+
+binary: $(DT_BIN)
+
+$(LIB): $(OBJS) $(DTB)
+ $(call cmd_link_o_target, $(OBJS))
+
+#########################################################################
+
+# defines $(obj).depend target
+include $(SRCTREE)/rules.mk
+
+sinclude $(obj).depend
+
+#########################################################################
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