[PATCH] scripts/Makefile.lib: add -D__U_BOOT__ to dtc_cpp_flags

[Tom Rini]

On Fri, Jul 01, 2022 at 09:27:59AM +0200, Rasmus Villemoes wrote:
> When trying to use the exact same device tree source to build the dtbs
> used with U-Boot and linux, one often runs into various problems. For
> example, files under include/dt-bindings/ might not be completely in
> sync, so some #defines are available in linux but not in U-Boot.
> 
> It's also possible that there are nodes/hardware one simply doesn't
> need or want to describe to U-Boot, e.g. to reduce the size of the
> .dtb (for SPL, there's already the whole fdtgrep machinery to deal
> with that, but not for U-Boot proper), or configuration settings like
> watchdog timeout one wants to make different between linux and U-Boot.
> 
> So in order to allow such tweaks, add an explicit define of the macro
> __U_BOOT__. Since U-Boot includes linux/kconfig.h (and defines
> __ASSEMBLY__ to make that work) while linux doesn't, one could also
> use __ASSEMBLY__ or just about any known-to-be-defined CONFIG_* macro
> as a proxy, but it's much more readable, maintainable and robust if
> one's .dts has "ifdef __U_BOOT__" rather than "ifdef __ASSEMBLY__".
> 
> Signed-off-by: Rasmus Villemoes <rasmus.villemoes at prevas.dk>
> ---
>  scripts/Makefile.lib | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index 3db2550085..4183767a62 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -190,6 +190,7 @@ dtc_cpp_flags  = -Wp,-MD,$(depfile).pre.tmp -nostdinc                    \
>  		 -I$(srctree)/arch/$(ARCH)/dts/include                   \
>  		 -I$(srctree)/include                                    \
>  		 -D__ASSEMBLY__                                          \
> +		 -D__U_BOOT__                                            \
>  		 -undef -D__DTS__
>  
>  # Finds the multi-part object the current object will be linked into

Since this implies to me using __U_BOOT__ in the main dts file itself,
we need to bring this up on devicetree-spec.  Otherwise, we could just
use the -u-boot.dtsi to remove nodes/properties, yes?  And then bindings
needing to be re-synced is something to incentivize, from my point of
view, initially at least.

-- 
Tom
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