[PATCH v2 1/1] kbuild: dtc: Allow adding device tree fragments via config

[Antony Pavlov]

On Wed, 22 Sep 2021 11:13:36 -0700
Trent Piepho <trent.piepho at igorinstitute.com> wrote:

Hi!

This patch was applied to barebox source tree as 
  
  2ae7ac7ab2 kbuild: dtc: Allow adding device tree fragments via config

With this patch I see build error if device tree file name starts with digit (0-9),
e.g.:

  barebox$ git checkout v2022.01.0

  barebox$ make mrproper

  barebox$ export ARCH=arm
  barebox$ export CROSS_COMPILE=arm-none-eabi-
  barebox$ sed -i "s/virt2real.dtb/2virt2real.dtb/" arch/arm/dts/Makefile
  barebox$ mv arch/arm/dts/virt2real.dts arch/arm/dts/2virt2real.dts

  barebox$ make virt2real_defconfig
  ...
  barebox$ make -s
  <stdin>:1:9: error: macro names must be identifiers                                              make[1]:  [scripts/Makefile.lib:352: arch/arm/dts/2virt2real.dtb] Error 1
  make:  [Makefile:952: arch/arm/dts] Error 2




> This introduces a config variable that allows adding additional fragments
> to the Barebox device tree(s).
> 
> Example uses are adjusting the flash partition layout, adding barebox
> state variables, or adding an I2C device.  These can be now be done with
> build configuration only, without needing to patch the existing dts
> files in the Barebox source.
> 
> The advantage is greater when an external build system, such as Yocto or
> Buildroot, is being used to build Barebox.  The build system can drop in
> a dts fragment to partition flash and build from unaltered Barebox
> source.  This avoids the need for cumbersome maintenance of patch files
> to modify Barebox's source for each flash partition layout.
> 
> Preprocessing the dts file gains another layer, where a generated dts
> source consisting of an include directive for the original dts source is
> followed by more includes for each fragment.  This is piped to the
> existing preprocessor call on stdin to avoid another temporary file.
> cpp/dtc will correctly identify errors in the source files they occur
> in.  The -MT option is used so the cpp auto-dependencies reference the
> original dts source and not the generated code passed on stdin.
> 
> A preprocessor macro named after the base dts file, e.g. foo-bar.dts
> will define foo_bar_dts, will be defined so that the fragments can
> possibly operate differently based on which image's dts is being built.
> 
> Signed-off-by: Trent Piepho <trent.piepho at igorinstitute.com>
> ---
> Changes from v1:
>   - Remove 2nd config variable for in-tree fragments.
>   - Add macro to preproccessed dts
> 
>  common/Kconfig       | 18 ++++++++++++++++++
>  scripts/Makefile.lib |  8 +++++++-
>  2 files changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/common/Kconfig b/common/Kconfig
> index a9feae2ae..6fdc14148 100644
> --- a/common/Kconfig
> +++ b/common/Kconfig
> @@ -1091,6 +1091,24 @@ config SYSTEMD_OF_WATCHDOG
>  	  in the kernel device tree. If the kernel is booted without a device
>  	  tree or with one that lacks aliases, nothing is added.
>  
> +config EXTERNAL_DTS_FRAGMENTS
> +	string "external dts file fragments"
> +	depends on OFTREE
> +	help
> +	  List of dts fragment files that will be appended to Barebox's device
> +	  tree(s) source when building the dtb file(s).  If multiple files are
> +	  listed, they will be appended in order.  Relative filenames will use
> +	  the dtc include search path.
> +
> +	  A preprocessor macro based on the name of the main dts will be
> +	  defined, which allows the dts fragments to based on which image of a
> +	  multi image build they are being used in.
> +
> +	  It not intended that this be put into into Barebox defconfig files.
> +	  Instead, it's an external build system, like Yocto or buildroot, to
> +	  add dts fragments from outside the Barebox source tree into the
> +	  Barebox build.
> +
>  menu "OP-TEE loading"
>  
>  config OPTEE_SIZE
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index 80d76b177..4496f1a70 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -201,6 +201,7 @@ cpp_flags      = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(__cpp_flags)
>  ld_flags       = $(KBUILD_LDFLAGS) $(ldflags-y)
>  
>  dtc_cpp_flags  = -Wp,-MD,$(depfile).pre -nostdinc                        \
> +		 -Wp,-MT,$(basename $(notdir $@)).o                      \
>  		 -I$(srctree)/arch/$(SRCARCH)/dts/include		 \
>  		 -I$(srctree)/dts/include                                \
>  		 -I$(srctree)/include                                    \
> @@ -335,8 +336,13 @@ cmd_dt_S_dtb = $(srctree)/scripts/gen-dtb-s $(subst -,_,$(*F)) $< $(CONFIG_IMD)
>  $(obj)/%.dtb.S: $(obj)/%.dtb $(srctree)/scripts/gen-dtb-s FORCE
>  	$(call if_changed,dt_S_dtb)
>  
> +dts-frags = $(subst $(quote),,$(CONFIG_EXTERNAL_DTS_FRAGMENTS))
>  quiet_cmd_dtc = DTC     $@
> -cmd_dtc = $(CPP) $(dtc_cpp_flags) -x assembler-with-cpp -o $(dtc-tmp) $< ; \
> +# For compatibility between make 4.2 and 4.3
> +H := \#
> +cmd_dtc = /bin/echo -e '$(H)define $(subst -,_,$(*F))_dts 1\n'$(foreach f,$< $(dts-frags),'$(H)include "$(f)"\n') | \
> +	$(CPP) $(dtc_cpp_flags) -x assembler-with-cpp -o $(dtc-tmp) - ; \
>  	$(objtree)/scripts/dtc/dtc -O dtb -o $@ -b 0 \
>  		-i $(srctree)/arch/$(SRCARCH)/dts $(DTC_FLAGS) \
>  		-i $(srctree)/dts/src/$(SRCARCH) \
> -- 
> 2.31.1
> 
> 
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-- 
Best regards,
  Antony Pavlov