Re: [PATCH v3 6/9] kbuild: consolidate Devicetree dtb build rules

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Yamada-san,

On Wed, Sep 12, 2018 at 3:02 AM Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
> 2018-09-12 0:40 GMT+09:00 Rob Herring <robh@kernel.org>:
> > On Mon, Sep 10, 2018 at 10:04 AM Rob Herring <robh@kernel.org> wrote:
> >> There is nothing arch specific about building dtb files other than their
> >> location under /arch/*/boot/dts/. Keeping each arch aligned is a pain.
> >> The dependencies and supported targets are all slightly different.
> >> Also, a cross-compiler for each arch is needed, but really the host
> >> compiler preprocessor is perfectly fine for building dtbs. Move the
> >> build rules to a common location and remove the arch specific ones. This
> >> is done in a single step to avoid warnings about overriding rules.
> >>
> >> The build dependencies had been a mixture of 'scripts' and/or 'prepare'.
> >> These pull in several dependencies some of which need a target compiler
> >> (specifically devicetable-offsets.h) and aren't needed to build dtbs.
> >> All that is really needed is dtc, so adjust the dependencies to only be
> >> dtc.
> >>
> >> This change enables support 'dtbs_install' on some arches which were
> >> missing the target.
> >
> > [...]
> >
> >> @@ -1215,6 +1215,33 @@ kselftest-merge:
> >>                 $(srctree)/tools/testing/selftests/*/config
> >>         +$(Q)$(MAKE) -f $(srctree)/Makefile olddefconfig
> >>
> >> +# ---------------------------------------------------------------------------
> >> +# Devicetree files
> >> +
> >> +ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/boot/dts/),)
> >> +dtstree := arch/$(SRCARCH)/boot/dts
> >> +endif
> >> +
> >> +ifdef CONFIG_OF_EARLY_FLATTREE
> >
> > This can be true when dtstree is unset. So this line should be this
> > instead to fix the 0-day reported error:
> >
> > ifneq ($(dtstree),)
> >
> >> +
> >> +%.dtb : scripts_dtc
> >> +       $(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@
> >> +
> >> +PHONY += dtbs dtbs_install
> >> +dtbs: scripts_dtc
> >> +       $(Q)$(MAKE) $(build)=$(dtstree)
> >> +
> >> +dtbs_install: dtbs
> >> +       $(Q)$(MAKE) $(dtbinst)=$(dtstree)
> >> +
> >> +all: dtbs
> >> +
> >> +endif
>
>
> Ah, right.
> Even x86 can enable OF and OF_UNITTEST.
>
>
>
> Another solution might be,
> guard it by 'depends on ARCH_SUPPORTS_OF'.
>
>
>
> This is actually what ACPI does.
>
> menuconfig ACPI
>         bool "ACPI (Advanced Configuration and Power Interface) Support"
>         depends on ARCH_SUPPORTS_ACPI
>          ...

ACPI is a real platform feature, as it depends on firmware.

CONFIG_OF can be enabled, and DT overlays can be loaded, on any platform,
even if it has ACPI ;-)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds