[PATCH v7 30/31] fdt: Avoid emitting an device tree when not needed

Simon Glass sjg at chromium.org
Tue Dec 7 01:12:08 CET 2021

U-Boot always needs some sort of a device tree. 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 at chromium.org>

(no changes since v1)

 Makefile    |  6 +++++-
 dts/Kconfig | 10 ++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 6671c5d9e2f..a3f018f01e0 100644
--- a/Makefile
+++ b/Makefile
@@ -952,7 +952,11 @@ INPUTS-$(CONFIG_SPL_FRAMEWORK) += u-boot.img
 INPUTS-$(CONFIG_TPL) += tpl/u-boot-tpl.bin
+# Allow omitting the .dtb output if it is not normally used
 INPUTS-$(CONFIG_OF_SEPARATE) += u-boot-dtb.img
@@ -1192,7 +1196,7 @@ 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)
 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 803d0899556..fd2829ad708 100644
--- 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.
 	string "Default Device Tree for DT control"
 	depends on OF_CONTROL

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