fdt: Add support for a separate device tree (CONFIG_OF_SEPARATE)

This adds support for an FDT to be build as a separate binary file called
u-boot.dtb. This can be concatenated with the U-Boot binary to provide a
device tree located at run-time by U-Boot. The Makefile is modified to
provide this file in u-boot-dtb.bin.

Signed-off-by: Simon Glass <sjg@chromium.org>

.gitignore

@@ -35,6 +35,7 @@
 /u-boot.dis
 /u-boot.lds
 /u-boot.ubl
+/u-boot.dtb
 
 #
 # Generated files

Makefile

@@ -359,9 +359,17 @@ ALL-$(CONFIG_ONENAND_U_BOOT) += $(obj)u-boot-onenand.bin
 ONENAND_BIN ?= $(obj)onenand_ipl/onenand-ipl-2k.bin
 ALL-$(CONFIG_MMC_U_BOOT) += $(obj)mmc_spl/u-boot-mmc-spl.bin
 ALL-$(CONFIG_SPL) += $(obj)spl/u-boot-spl.bin
+ALL-$(CONFIG_OF_SEPARATE) += $(obj)u-boot.dtb $(obj)u-boot-dtb.bin
 
 all:		$(ALL-y) $(SUBDIR_EXAMPLES)
 
+$(obj)u-boot.dtb:	$(obj)u-boot
+		$(MAKE) -C dts binary
+		mv $(obj)dts/dt.dtb $@
+
+$(obj)u-boot-dtb.bin:	$(obj)u-boot.bin $(obj)u-boot.dtb
+		cat $^ >$@
+
 $(obj)u-boot.hex:	$(obj)u-boot
 		$(OBJCOPY) ${OBJCFLAGS} -O ihex $< $@
 

README

@@ -824,8 +824,8 @@ The following options need to be configured:
 		experimental and only available on a few boards. The device
 		tree is available in the global data as gd->fdt_blob.
 
-		U-Boot needs to get its device tree from somewhere. At present
-		the only way is to embed it in the image with CONFIG_OF_EMBED.
+		U-Boot needs to get its device tree from somewhere. This can
+		be done using one of the two options below:
 
 		CONFIG_OF_EMBED
 		If this variable is defined, U-Boot will embed a device tree
@@ -834,6 +834,18 @@ The following options need to be configured:
 		is then picked up in board_init_f() and made available through
 		the global data structure as gd->blob.
 
+		CONFIG_OF_SEPARATE
+		If this variable is defined, U-Boot will build a device tree
+		binary. It will be called u-boot.dtb. Architecture-specific
+		code will locate it at run-time. Generally this works by:
+
+			cat u-boot.bin u-boot.dtb >image.bin
+
+		and in fact, U-Boot does this for you, creating a file called
+		u-boot-dtb.bin which is useful in the common case. You can
+		still use the individual files if you need something more
+		exotic.
+
 - Watchdog:
 		CONFIG_WATCHDOG
 		If this variable is defined, it enables watchdog