[Buildroot] [PATCH v2] boot/uboot: support custom DTS with CONFIG_OF_UPSTREAM

[Alexander Sverdlin <alexander.sverdlin@gmail.com>]

Since U-Boot 2024.07, boards with CONFIG_OF_UPSTREAM build their device
trees from dts/upstream/src/<arch>/<vendor>/ instead of arch/<arch>/dts/,
so the files copied by BR2_TARGET_UBOOT_CUSTOM_DTS_PATH were ignored and
the build failed with "No rule to make target".

Derive the destination from the U-Boot configuration, including the vendor
sub-directory taken from CONFIG_DEFAULT_DEVICE_TREE. That tree keeps the
Linux architecture naming, so aarch64 has to be mapped back from
UBOOT_ARCH ("arm") to "arm64".

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
---
Changelog:
v2:
- handle *u-boot.dtsi separately
- document the new behaviour with OF_UPSTREAM-enabled U-Boot builds
v1:
https://lore.kernel.org/all/20260901145225.579733-1-alexander.sverdlin@gmail.com/

 boot/uboot/Config.in | 13 +++++++++++--
 boot/uboot/uboot.mk  | 30 +++++++++++++++++++++++++++---
 2 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/boot/uboot/Config.in b/boot/uboot/Config.in
index 1eabd10407..1795f22b20 100644
--- a/boot/uboot/Config.in
+++ b/boot/uboot/Config.in
@@ -803,8 +803,17 @@ config BR2_TARGET_UBOOT_CUSTOM_DTS_PATH
 	string "Device Tree Source file paths"
 	help
 	  Space-separated list of paths to device tree source files
-	  that will be copied to arch/ARCH/dts/ before starting the
-	  build.
+	  that will be copied before starting the build.
+
+	  They are copied to arch/ARCH/dts/, except that a configuration
+	  with CONFIG_OF_UPSTREAM (U-Boot 2024.07 and later) builds its
+	  device trees from the vendor directory below dts/upstream/src/
+	  that CONFIG_DEFAULT_DEVICE_TREE names, so they are copied
+	  there instead.
+
+	  The *u-boot.dtsi fragments U-Boot includes on its own are
+	  copied to arch/ARCH/dts/ in either case, as that is the only
+	  place it looks for them.
 
 	  To use this device tree source file, the U-Boot configuration
 	  file must refer to it.
diff --git a/boot/uboot/uboot.mk b/boot/uboot/uboot.mk
index 5b3f46ac74..1453308c17 100644
--- a/boot/uboot/uboot.mk
+++ b/boot/uboot/uboot.mk
@@ -426,10 +426,34 @@ endif # BR2_TARGET_UBOOT_BUILD_SYSTEM_LEGACY
 
 UBOOT_CUSTOM_DTS_PATH = $(call qstrip,$(BR2_TARGET_UBOOT_CUSTOM_DTS_PATH))
 
+# With CONFIG_OF_UPSTREAM the device trees are built from dts/upstream/src/
+# instead of arch/<arch>/dts/, in the vendor sub-directory encoded in the
+# device tree name. That tree keeps the Linux architecture naming, so aarch64
+# has to be mapped back from UBOOT_ARCH ("arm") to "arm64". The fragments
+# U-Boot includes on its own are searched for in arch/<arch>/dts/ only, so
+# they stay there whatever the device trees do.
+define UBOOT_INSTALL_CUSTOM_DTS
+	arch_dir="arch/$(UBOOT_ARCH)/dts"; \
+	dts_dir="$$arch_dir"; \
+	if grep -q "^CONFIG_OF_UPSTREAM=y" $(@D)/.config; then \
+		if grep -q "^CONFIG_ARM64=y" $(@D)/.config; then \
+			dts_dir="dts/upstream/src/arm64"; \
+		else \
+			dts_dir="dts/upstream/src/$(UBOOT_ARCH)"; \
+		fi; \
+		dt=$$(sed -n 's/^CONFIG_DEFAULT_DEVICE_TREE="\(.*\)"$$/\1/p' $(@D)/.config); \
+		case "$$dt" in */*) dts_dir="$$dts_dir/$${dt%/*}";; esac; \
+	fi; \
+	for dts in $(UBOOT_CUSTOM_DTS_PATH); do \
+		case "$$dts" in \
+		*u-boot.dtsi) cp -f "$$dts" $(@D)/$$arch_dir/;; \
+		*) cp -f "$$dts" $(@D)/$$dts_dir/;; \
+		esac; \
+	done
+endef
+
 define UBOOT_BUILD_CMDS
-	$(if $(UBOOT_CUSTOM_DTS_PATH),
-		cp -f $(UBOOT_CUSTOM_DTS_PATH) $(@D)/arch/$(UBOOT_ARCH)/dts/
-	)
+	$(if $(UBOOT_CUSTOM_DTS_PATH),$(UBOOT_INSTALL_CUSTOM_DTS))
 	$(TARGET_CONFIGURE_OPTS) \
 		PKG_CONFIG="$(PKG_CONFIG_HOST_BINARY)" \
 		PKG_CONFIG_SYSROOT_DIR="/" \
-- 
2.55.0

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