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-rw-r--r--Documentation/kbuild/makefiles.txt23
-rw-r--r--scripts/Makefile.lib10
2 files changed, 33 insertions, 0 deletions
diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
index 14c3f4f1b617..5198b742fde1 100644
--- a/Documentation/kbuild/makefiles.txt
+++ b/Documentation/kbuild/makefiles.txt
@@ -1186,6 +1186,29 @@ When kbuild executes, the following steps are followed (roughly):
clean-files += *.dtb
DTC_FLAGS ?= -p 1024
+ dtc_cpp
+ This is just like dtc as describe above, except that the C pre-
+ processor is invoked upon the .dtsp file before compiling the result
+ with dtc.
+
+ In order for build dependencies to work, all files compiled using
+ dtc_cpp must use the C pre-processor's #include functionality and not
+ dtc's /include/ functionality.
+
+ Using the C pre-processor allows use of #define to create named
+ constants. In turn, the #defines will typically appear in a header
+ file, which may be shared with regular C code. Since the dtc language
+ represents a data structure rather than code in C syntax, similar
+ restrictions are placed on a header file included by a device tree
+ file as for a header file included by an assembly language file.
+ In particular, the C pre-processor is passed -x assembler-with-cpp,
+ which sets macro __ASSEMBLY__. __DTS__ is also set. These allow header
+ files to restrict their content to that compatible with device tree
+ source.
+
+ A central rule exists to create $(obj)/%.dtb from $(src)/%.dtsp;
+ architecture Makefiles do no need to explicitly write out that rule.
+
--- 6.8 Custom kbuild commands
When kbuild is executing with KBUILD_VERBOSE=0, then only a shorthand
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index bdf42fdf64c9..7910229ec665 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -269,6 +269,16 @@ cmd_dtc = $(objtree)/scripts/dtc/dtc -O dtb -o $@ -b 0 $(DTC_FLAGS) -d $(depfile
$(obj)/%.dtb: $(src)/%.dts FORCE
$(call if_changed_dep,dtc)
+dtc-tmp = $(subst $(comma),_,$(dot-target).dts)
+
+quiet_cmd_dtc_cpp = DTC+CPP $@
+cmd_dtc_cpp = $(CPP) $(cpp_flags) -x assembler-with-cpp -undef -D__DTS__ \
+ -o $(dtc-tmp) $< ; \
+ $(objtree)/scripts/dtc/dtc -O dtb -o $@ -b 0 $(DTC_FLAGS) $(dtc-tmp)
+
+$(obj)/%.dtb: $(src)/%.dtsp FORCE
+ $(call if_changed_dep,dtc_cpp)
+
# Bzip2
# ---------------------------------------------------------------------------