kbuild: create a rule to run the pre-processor on *.dts files

Create cmd_dtc_cpp to run the C pre-processor on *.dts file before
passing them to dtc for final compilation. This allows the use of #define
and #include within the .dts file.

Acked-by: Simon Glass <sjg@chromium.org>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Acked-by: Michal Marek <mmarek@suse.cz>
Acked-by: Srinivas Kandagatla <srinivas.kandagatla@st.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
index 14c3f4f..5198b74 100644 (file)
--- 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 bdf42fd..7910229 100644 (file)
--- 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)
+
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