linux-kernel - Re: [PATCH V2 REPOST] kbuild: create an "include chroot" for DT bindings

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Message-ID: <5136E866.20008@gmail.com>
Date:	Wed, 06 Mar 2013 00:55:34 -0600
From:	Rob Herring <robherring2@...il.com>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	Grant Likely <grant.likely@...retlab.ca>,
	Michal Marek <mmarek@...e.cz>,
	Stephen Warren <swarren@...dia.com>,
	linux-kbuild@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Hiroshi Doyu <hdoyu@...dia.com>,
	"arm@...nel.org" <arm@...nel.org>
Subject: Re: [PATCH V2 REPOST] kbuild: create an "include chroot" for DT bindings

On 03/05/2013 12:06 PM, Stephen Warren wrote:
> From: Stephen Warren <swarren@...dia.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, most 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 -> ../../../../../include/dt-bindings
> 
> Some headers used by device tree files may not be useful to the kernel;
> they may be used simply to aid in constructing the DT file (e.g. macros
> to create a node), but not define any information that the kernel needs
> to share. These may be placed directly into arch/*/boot/dts/ along with
> the DT files themselves.
> 
> Cc: Hiroshi Doyu <hdoyu@...dia.com>
> Acked-by: Michal Marek <mmarek@...e.cz>
> Acked-by: Shawn Guo <shawn.guo@...aro.org>
> Signed-off-by: Stephen Warren <swarren@...dia.com>
> ---
> Grant, Rob,
> 
> This is a pre-requisite for people to convert their *.dts files to use
> cpp, and hence is likely to be useful for a number of ARM subarch trees.
> Perhaps this patch can be placed into a standalone topic branch in the
> DT repo so we can all merge it. Assuming this patch is OK, I would also
> repost the patches that create common headers defining IRQ, and GPIO
> flags, which would place files into the new include/dt-bindings
> directory.

This looks fine to me. As all these will all be arm-soc branches with
the dependency, it probably makes more sense for Arnd/Olof to apply this
and create the branch for this single patch.

Acked-by: Rob Herring <rob.herring@...xeda.com>

Rob

> 
> v2:
> * Leave arch/*/boot/dts in dtc include path, for any headers that are
>   only included by *.dts and don't need to be shared by the kernel.
> * Fix pathname in commit description.
> ---
>  arch/arm/boot/dts/include/dt-bindings |    1 +
>  scripts/Makefile.lib                  |    2 +-
>  2 files changed, 2 insertions(+), 1 deletion(-)
>  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..af35521 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -158,7 +158,7 @@ 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
> 

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