[PATCH] kbuild: create an "include chroot" for DT bindings

[Stephen Warren]

From: Stephen Warren <swarren at nvidia.com>

The recent dtc+cpp support allows header files and C pre-processor
defines/macros to be used when compiling device tree files. These
headers will typically define various constants that are part of the
device tree bindings.

The original patch which set up the dtc+cpp include path only considered
using those headers from device tree files. However, they are also
useful for kernel code which needs to interpret the device tree.

In both the DT files and the kernel, I'd like to include the DT-related
headers in the same way, for example, <dt-bindings/gpio/tegra-gpio.h>.
That will simplify any text which discusses the DT header locations.

Creating a <dt-bindings/> for kernel source to use is as simple as
placing files into include/dt-bindings/.

However, when compiling DT files, the include path should be restricted
so that only the dt-bindings path is available; arbitrary kernel headers
shouldn't be exposed. For this reason, create a specific include
directory for use by dtc+cpp, and symlink dt-bindings from there to the
actual location of include/dt-bindings/. For want of a better location,
place this "include chroot" into the existing dts/ directory.

arch/*/boot/dts/include/dt-bindings -> ../../../../../dt-bindings

Cc: Shawn Guo <shawn.guo at linaro.org>
Cc: Hiroshi Doyu <hdoyu at nvidia.com>
Signed-off-by: Stephen Warren <swarren at nvidia.com>
---
You can find an example of how this would be used at
git://nv-tegra.nvidia.com/user/swarren/linux-2.6 linux-next_common
(note: there's a bunch of other cruft in that branch too)

 arch/arm/boot/dts/include/dt-bindings |    1 +
 scripts/Makefile.lib                  |    3 +--
 2 files changed, 2 insertions(+), 2 deletions(-)
 create mode 120000 arch/arm/boot/dts/include/dt-bindings

diff --git a/arch/arm/boot/dts/include/dt-bindings b/arch/arm/boot/dts/include/dt-bindings
new file mode 120000
index 0000000..08c00e4
--- /dev/null
+++ b/arch/arm/boot/dts/include/dt-bindings
@@ -0,0 +1 @@
+../../../../../include/dt-bindings
\ No newline at end of file
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 07125e6..d6c5036 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -157,8 +157,7 @@ cpp_flags      = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(LINUXINCLUDE)     \
 ld_flags       = $(LDFLAGS) $(ldflags-y)
 
 dtc_cpp_flags  = -Wp,-MD,$(depfile) -nostdinc                            \
-		 -I$(srctree)/arch/$(SRCARCH)/boot/dts                   \
-		 -I$(srctree)/arch/$(SRCARCH)/include/dts                \
+		 -I$(srctree)/arch/$(SRCARCH)/boot/dts/include           \
 		 -undef -D__DTS__
 
 # Finds the multi-part object the current object will be linked into
-- 
1.7.10.4