[RESEND PATCHv2 2/4] ARM: dts: add support for individual build flags for DT subdirs

[frowand.list@gmail.com (Frank Rowand)]

On 09/04/18 01:05, Tero Kristo wrote:
> Currently the makefile is setup in such manner that even if
> we build a DT file in a subdirectory under arch/arm/boot/dts,
> it gets built based on the base boot/dts/Makefile rules.
> This patch modifies the base makefile in such manner, that
> it detects which makefile to use based on build target path.
> This allows setting for example per-directory DTC_FLAGS and
> using those for the subdir build. The dtbdir local variable
> is setup to target to the build path.
> 
> Signed-off-by: Tero Kristo <t-kristo@ti.com>
> ---
>  arch/arm/Makefile | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/Makefile b/arch/arm/Makefile
> index ab555a0..b7c21e8 100644
> --- a/arch/arm/Makefile
> +++ b/arch/arm/Makefile
> @@ -339,8 +339,10 @@ $(BOOT_TARGETS): vmlinux
>  $(INSTALL_TARGETS):
>  	$(Q)$(MAKE) $(build)=$(boot) MACHINE=$(MACHINE) $@
>  
> +%.dtb %.dtbo: dtbdir = $(patsubst %/,%,$(patsubst %./,%,$(boot)/dts/$(dir $@)))
> +
>  %.dtb %.dtbo: | scripts
> -	$(Q)$(MAKE) $(build)=$(boot)/dts MACHINE=$(MACHINE) $(boot)/dts/$@
> +	$(Q)$(MAKE) $(build)=$(dtbdir) MACHINE=$(MACHINE) $(boot)/dts/$@
>  
>  PHONY += dtbs dtbs_install
>  
> 

The makefile magic to handle subdirectories below $(boot)/dts/ already
works properly to have Makefiles in $(boot)/dts/, using the following
rule in arch/arm64/Makefile:

%.dtb: scripts
        $(Q)$(MAKE) $(build)=$(boot)/dts $(boot)/dts/$@

I don't understand why that works for arm64, but it should work the
same way for arm.  Or if arch/arm is missing another piece from
arch/arm64 we should be consistent with however the make system
specifies it in arch/arm64