Merge branch 'tip/perf/urgent-2' of git://git.kernel.org/pub/scm/linux/kernel/git...

[sfrench/cifs-2.6.git] / Documentation / kbuild / makefiles.txt

diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
index 14c3f4f1b61773bc660f1f73a1c57e438f2ef975..5198b742fde1608330b799015573ecf97277531e 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