linux-kernel - Re: [PATCH V7] kbuild: create a rule to run the pre-processor on *.dts files

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Date:	Mon, 14 Jan 2013 15:53:22 +0100
From:	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Grant Likely <glikely@...retlab.ca>,
	David Gibson <david@...son.dropbear.id.au>,
	Michal Marek <mmarek@...e.cz>, Jon Loeliger <jdl@....com>,
	Rob Herring <rob.herring@...xeda.com>,
	Scott Wood <scottwood@...escale.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Sam Ravnborg <sam@...nborg.org>,
	Simon Glass <sjg@...omium.org>, linux-kernel@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org,
	Stephen Warren <swarren@...dia.com>
Subject: Re: [PATCH V7] kbuild: create a rule to run the pre-processor on
 *.dts files

On 11:43 Wed 02 Jan     , Stephen Warren wrote:
> From: Stephen Warren <swarren@...dia.com>
> 
> 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.
> 
> Signed-off-by: Stephen Warren <swarren@...dia.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>

Best Regards,
J.
> ---
> Grant, back in mid-November, you said you'd make a decision on this in
> the next couple of days, but I think this got overlooked.
> 
> v7: Build *.dtb from *.dts not src/*.dts.
> v6: No change.
> v5:
> * Update Documentation/kbuild for the new command and rule.
> v4:
> * Use -x assembler-with-cpp so pre-defined macros are set up so that
>   #included header files know to only use cpp syntax, not C syntax.
> * Define __DTS__ for similar reasons.
> * use $(CPP) not $(CC) -E, and use $(cpp_flags).
> * Save the pre-processed results so they can be easily inspected when
>   debugging build issues.
> * The use of -x assembler-with-cpp causes cpp to recognize directives in
>   column 1 only. Hence, there's no need to escape property names that
>   begin with #. Hence, there's no need for separate skeleton.dtsi and
>   skeleton.dtsip. Maintain a separate file extension and build rule so that
>   CPP-usage is opt-in. In particular, when using CPP, #include must be used
>   rather than /include/ so that dependencies work.
> v3: Pass "-x c" not "-xc" to cpp.
> v2: Place make %.dtb: %.dtsp rule into Makefile.lib.
> ---
>  Documentation/kbuild/makefiles.txt |   23 +++++++++++++++++++++++
>  scripts/Makefile.lib               |    9 +++++++++
>  2 files changed, 32 insertions(+)
> 
> diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
> index 14c3f4f..5198b74 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 bdf42fd..2c2a302 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -269,6 +269,15 @@ 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) -D__DTS__ -x assembler-with-cpp -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
>  # ---------------------------------------------------------------------------
>  
> -- 
> 1.7.10.4
> 
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