fdt: Avoid emitting an device tree when not needed

U-Boot always needs some sort of a device tree in the build. Some boards
never actually use this, at least in production systems, since a prior
firmware stage sets one up and passes it to U-Boot. At present the only
mechanism to do that is with custom function (OF_BOARD), but future work
will include a standard way of doing this ('standard passage').

It can be confusing to see a device tree emitted from the U-Boot build in
this situation. Add an option to drop it.

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

diff --git a/Makefile b/Makefile
index a4f267c..074ba73 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -944,7 +944,9 @@ INPUTS-$(CONFIG_SPL_FRAMEWORK) += u-boot.img
 endif
 endif
 INPUTS-$(CONFIG_TPL) += tpl/u-boot-tpl.bin
-INPUTS-$(CONFIG_OF_SEPARATE) += u-boot.dtb
+
+# Allow omitting the .dtb output if it is not normally used
+INPUTS-$(CONFIG_OF_SEPARATE) += $(if $(CONFIG_OF_OMIT_DTB),dts/dt.dtb,u-boot.dtb)
 ifeq ($(CONFIG_SPL_FRAMEWORK),y)
 INPUTS-$(CONFIG_OF_SEPARATE) += u-boot-dtb.img
 endif
@@ -1187,7 +1189,7 @@ u-boot.bin: u-boot-fit-dtb.bin FORCE
 u-boot-dtb.bin: u-boot-nodtb.bin dts/dt.dtb FORCE
        $(call if_changed,cat)
 
-else ifeq ($(CONFIG_OF_SEPARATE),y)
+else ifeq ($(CONFIG_OF_SEPARATE).$(CONFIG_OF_OMIT_DTB),y.)
 u-boot-dtb.bin: u-boot-nodtb.bin dts/dt.dtb FORCE
        $(call if_changed,cat)
 

diff --git a/dts/Kconfig b/dts/Kconfig
index e57ce84..fb7df53 100644 (file)
--- a/dts/Kconfig
+++ b/dts/Kconfig
@@ -129,6 +129,16 @@ config OF_HAS_PRIOR_STAGE
          Note: This option must be set in Kconfig and cannot be enabled or
          disabled in the board's defconfig file.
 
+config OF_OMIT_DTB
+       bool "Omit the device tree output when building"
+       default y if OF_HAS_PRIOR_STAGE && !BINMAN
+       help
+         As a special case, avoid writing a device tree file u-boot.dtb when
+         building. Also don't include that file in u-boot.bin
+
+         This is used for boards which normally provide a devicetree via a
+         runtime mechanism (such as OF_BOARD), to avoid confusion.
+
 config DEFAULT_DEVICE_TREE
        string "Default Device Tree for DT control"
        depends on OF_CONTROL