include/image*: add support for device-tree overlays

Add new target feature 'dt-overlay' which makes DTC keep the symbol
names in the generated dtb.
Make sure additional DT overlay sources specified by the new device
variable DEVICE_DTS_OVERLAY get compiled together with the main DTS
(currently overlays got to be in the same folder). Let Build/fit pass
the generated DT overlay blobs to mkits.sh.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

include/image-commands.mk

@@ -207,13 +207,16 @@ endef
 define Build/fit
 	$(TOPDIR)/scripts/mkits.sh \
 		-D $(DEVICE_NAME) -o $@.its -k $@ \
-		$(if $(word 2,$(1)),-d $(word 2,$(1))) -C $(word 1,$(1)) \
+		-C $(word 1,$(1)) $(if $(word 2,$(1)),\
+		$(if $(DEVICE_DTS_OVERLAY),-d $(KERNEL_BUILD_DIR)/image-$$(basename $(word 2,$(1))),\
+			-d $(word 2,$(1)))) \
 		$(if $(findstring with-rootfs,$(word 3,$(1))),-r $(IMAGE_ROOTFS)) \
 		$(if $(findstring with-initrd,$(word 3,$(1))), \
 			$(if $(CONFIG_TARGET_ROOTFS_INITRAMFS_SEPARATE), \
 				-i $(KERNEL_BUILD_DIR)/initrd.cpio$(strip $(call Build/initrd_compression)))) \
 		-a $(KERNEL_LOADADDR) -e $(if $(KERNEL_ENTRY),$(KERNEL_ENTRY),$(KERNEL_LOADADDR)) \
 		$(if $(DEVICE_FDT_NUM),-n $(DEVICE_FDT_NUM)) \
+		$(if $(DEVICE_DTS_OVERLAY),$(foreach dtso,$(DEVICE_DTS_OVERLAY), -O $(dtso):$(KERNEL_BUILD_DIR)/image-$(dtso).dtb)) \
 		-c $(if $(DEVICE_DTS_CONFIG),$(DEVICE_DTS_CONFIG),"config-1") \
 		-A $(LINUX_KARCH) -v $(LINUX_VERSION)
 	PATH=$(LINUX_DIR)/scripts/dtc:$(PATH) mkimage $(if $(findstring external,$(word 3,$(1))),\

include/image.mk

@@ -190,6 +190,7 @@ define Image/BuildDTB
 		-o $(2).tmp $(1)
 	$(LINUX_DIR)/scripts/dtc/dtc -O dtb \
 		-i$(dir $(1)) $(DTC_FLAGS) $(4) \
+	$(if $(CONFIG_HAS_DT_OVERLAY_SUPPORT),-@) \
 		-o $(2) $(2).tmp
 	$(RM) $(2).tmp
 endef
@@ -393,6 +394,7 @@ define Device/Init
   DEVICE_DTS :=
   DEVICE_DTS_CONFIG :=
   DEVICE_DTS_DIR :=
+  DEVICE_DTS_OVERLAY :=
   DEVICE_FDT_NUM :=
   SOC :=
 
@@ -416,8 +418,8 @@ DEFAULT_DEVICE_VARS := \
   DEVICE_NAME KERNEL KERNEL_INITRAMFS KERNEL_INITRAMFS_IMAGE KERNEL_SIZE \
   CMDLINE UBOOTENV_IN_UBI KERNEL_IN_UBI BLOCKSIZE PAGESIZE SUBPAGESIZE \
   VID_HDR_OFFSET UBINIZE_OPTS UBINIZE_PARTS MKUBIFS_OPTS DEVICE_DTS \
-  DEVICE_DTS_CONFIG DEVICE_DTS_DIR DEVICE_FDT_NUM SOC BOARD_NAME \
-  UIMAGE_MAGIC UIMAGE_NAME \
+  DEVICE_DTS_CONFIG DEVICE_DTS_DIR DEVICE_DTS_OVERLAY DEVICE_FDT_NUM \
+  SOC BOARD_NAME UIMAGE_MAGIC UIMAGE_NAME \
   SUPPORTED_DEVICES IMAGE_METADATA KERNEL_ENTRY KERNEL_LOADADDR \
   UBOOT_PATH IMAGE_SIZE \
   DEVICE_COMPAT_VERSION DEVICE_COMPAT_MESSAGE \
@@ -539,7 +541,7 @@ endef
 endif
 
 define Device/Build/kernel
-  $$(eval $$(foreach dts,$$(DEVICE_DTS), \
+  $$(eval $$(foreach dts,$$(DEVICE_DTS) $$(DEVICE_DTS_OVERLAY), \
 	$$(call Device/Build/dtb,$$(notdir $$(dts)), \
 		$$(if $$(DEVICE_DTS_DIR),$$(DEVICE_DTS_DIR),$$(DTS_DIR)), \
 		$$(dts) \

scripts/target-metadata.pl

@@ -45,6 +45,7 @@ sub target_config_features(@) {
 		/^rootfs-part$/ and $ret .= "\tselect USES_ROOTFS_PART\n";
 		/^boot-part$/ and $ret .= "\tselect USES_BOOT_PART\n";
 		/^testing-kernel$/ and $ret .= "\tselect HAS_TESTING_KERNEL\n";
+		/^dt-overlay$/ and $ret .= "\tselect HAS_DT_OVERLAY_SUPPORT\n";
 	}
 	return $ret;
 }

target/Config.in

@@ -13,6 +13,9 @@ config HAS_SPE_FPU
 config HAS_FPU
 	bool
 
+config HAS_DT_OVERLAY_SUPPORT
+	bool
+
 config AUDIO_SUPPORT
 	bool