[S] Change in coreboot[main]: arch/riscv: Add common FDT build

[Maximilian Brune (Code Review)]

Maximilian Brune has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/83848?usp=email )

Change subject: arch/riscv: Add common FDT build
......................................................................

arch/riscv: Add common FDT build

Currently all platforms on RISC-V require a FDT.
The inclusion of the FDT is currently done in the platform Makefiles.
In order to factor out some common code this patch adds the inclusion
in the architecture Makefile.

Signed-off-by: Maximilian Brune 
Change-Id: I3b304a89646fe84c98e9f199f315bebb156de16c
---
M src/arch/riscv/Kconfig
M src/arch/riscv/Makefile.mk
2 files changed, 37 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/48/83848/1

diff --git a/src/arch/riscv/Kconfig b/src/arch/riscv/Kconfig
index 7bf643f..9a2d54e 100644
--- a/src/arch/riscv/Kconfig
+++ b/src/arch/riscv/Kconfig
@@ -134,4 +134,19 @@
    bool
    default y

+config RISCV_DTS
+	bool
+	default n
+	help
+	  This option is selected by mainboards that include a devicetree
+	  source file (not to be confused with the coreboot devicetree.cb files).
+	  The devicetree will be preprocessed and compiled into a FDT (flattened devicetree).
+	  Said FDT will be put into a CBFS file for use in runtime.
+
+config RISCV_DTS_FILE
+	string
+	depends on RISCV_DTS
+	help
+	  Path to the devicetree source file in .dts format.
+
 endif # if ARCH_RISCV
diff --git a/src/arch/riscv/Makefile.mk b/src/arch/riscv/Makefile.mk
index 05407f8..c2e8023 100644
--- a/src/arch/riscv/Makefile.mk
+++ b/src/arch/riscv/Makefile.mk
@@ -67,6 +67,28 @@
    $(top)/src/lib/memset.c
 all-$(CONFIG_RISCV_USE_ARCH_TIMER) += arch_timer.c

+## FDT (Flattened Devicetree) inclusion
+
+ifeq ($(CONFIG_RISCV_DTS),y)
+
+# at some point dtc may be compiled by our toolchain
+DTC ?= dtc
+CPPFLAGS_dts += -nostdinc -P -x assembler-with-cpp -I src/arch/riscv/include
+
+$(obj)/preprocessed.dts: $(call strip_quotes, $(CONFIG_RISCV_DTS_FILE))
+	$(CPP_riscv) $(CPPFLAGS_dts) -o $@ $<
+
+$(obj)/dtb: $(obj)/preprocessed.dts
+	$(DTC) -I dts -O dtb -o $@ $<
+
+# This may be optimized in the future by letting cbfstool parse our FDT into a unflattened
+# devicetree blob in build time, so that we only need to flatten it in runtime instead of
+# unflatten and flatten it in runtime.
+cbfs-files-y += DTB
+DTB-file := $(obj)/dtb
+DTB-type := raw
+
+endif # CONFIG_RISCV_DTS

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