2018-08-27 8:56 GMT+09:00 Rob Herring <robh at kernel.org>:
> On Sat, Aug 25, 2018 at 9:06 PM Masahiro Yamada
> <yamada.masahiro at socionext.com> wrote:
>>
>> Hi Rob,
>>
>>
>> 2018-08-22 6:55 GMT+09:00 Rob Herring <robh at kernel.org>:
>> > 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.
>> >
>> > Cc: Masahiro Yamada <yamada.masahiro at socionext.com>
>> > Cc: Michal Marek <michal.lkml at markovi.net>
>> > Cc: Vineet Gupta <vgupta at synopsys.com>
>> > Cc: Russell King <linux at armlinux.org.uk>
>> > Cc: Catalin Marinas <catalin.marinas at arm.com>
>> > Cc: Will Deacon <will.deacon at arm.com>
>> > Cc: Yoshinori Sato <ysato at users.sourceforge.jp>
>> > Cc: Michal Simek <monstr at monstr.eu>
>> > Cc: Ralf Baechle <ralf at linux-mips.org>
>> > Cc: Paul Burton <paul.burton at mips.com>
>> > Cc: James Hogan <jhogan at kernel.org>
>> > Cc: Ley Foon Tan <lftan at altera.com>
>> > Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
>> > Cc: Paul Mackerras <paulus at samba.org>
>> > Cc: Michael Ellerman <mpe at ellerman.id.au>
>> > Cc: Chris Zankel <chris at zankel.net>
>> > Cc: Max Filippov <jcmvbkbc at gmail.com>
>> > Cc: linux-kbuild at vger.kernel.org
>> > Cc: linux-snps-arc at lists.infradead.org
>> > Cc: linux-arm-kernel at lists.infradead.org
>> > Cc: uclinux-h8-devel at lists.sourceforge.jp
>> > Cc: linux-mips at linux-mips.org
>> > Cc: nios2-dev at lists.rocketboards.org
>> > Cc: linuxppc-dev at lists.ozlabs.org
>> > Cc: linux-xtensa at linux-xtensa.org
>> > Signed-off-by: Rob Herring <robh at kernel.org>
>> > ---
>> > Makefile | 30 ++++++++++++++++++++++++++++++
>> > arch/arc/Makefile | 6 ------
>> > arch/arm/Makefile | 20 +-------------------
>> > arch/arm64/Makefile | 17 +----------------
>> > arch/c6x/Makefile | 2 --
>> > arch/h8300/Makefile | 11 +----------
>> > arch/microblaze/Makefile | 4 +---
>> > arch/mips/Makefile | 15 +--------------
>> > arch/nds32/Makefile | 2 +-
>> > arch/nios2/Makefile | 7 -------
>> > arch/nios2/boot/Makefile | 4 ----
>> > arch/powerpc/Makefile | 3 ---
>> > arch/xtensa/Makefile | 12 +-----------
>> > scripts/Makefile | 1 -
>> > scripts/Makefile.lib | 2 +-
>> > 15 files changed, 38 insertions(+), 98 deletions(-)
>> >
>> > diff --git a/Makefile b/Makefile
>> > index c13f8b85ba60..6d89e673f192 100644
>> > --- a/Makefile
>> > +++ b/Makefile
>> > @@ -1212,6 +1212,30 @@ kselftest-merge:
>> > $(srctree)/tools/testing/selftests/*/config
>> > +$(Q)$(MAKE) -f $(srctree)/Makefile olddefconfig
>> >
>> > +# ---------------------------------------------------------------------------
>> > +# Devicetree files
>> > +
>> > +dtstree := $(wildcard arch/$(SRCARCH)/boot/dts)
>
> BTW, there's an error here too. It doesn't work right with
> KBUILD_OUTPUT set and should be:
>
> ifneq ($(wildcard $(srctree)/arch/$(SRCARCH)/boot/dts/),)
> dtstree := arch/$(SRCARCH)/boot/dts
> endif
>
>> > +
>> > +ifdef CONFIG_OF_EARLY_FLATTREE
>> > +
>> > +%.dtb %.dtb.S %.dtb.o: | dtc
>>
>> I think the pipe operator is unnecessary
>> because Kbuild will descend to $(dtstree) anyway.
>
> The pipe means 'order-only', right?
Yes.
> So it is just a weaker dependency
> for things which are not input files as dtc is not. The 'dtc' here is
> just the dtc rule below, not the actual executable. Or am I missing
> something?
The pipe is used when
- we want to make sure the weaker prerequisite exists
- but, we do not want to execute the recipe
even if the weaker prerequisite is updated
In this case, we want to execute the recipe _all_the_time_.
We compare the timestamp between %.dtb and %.dts in the sub-directory.
We never know the real depenency until the following recipe is run
$(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@
PHONY += dtbs
dtbs: | dtc
$(Q)$(MAKE) $(build)=$(dtstree)
Here 'dtbs' is a PHONY target.
We always want to run the recipe.
The pipe operator is not sensible.
--
Best Regards
Masahiro Yamada
