linux-kernel - Re: [PATCH] kbuild: add dtbs

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Date:   Sat, 23 Jul 2022 09:33:03 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nicolas Schier <nicolas@...sle.eu>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>, Rob Herring <robh@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kbuild: add dtbs_prepare target

On Fri, Jul 22, 2022 at 7:14 PM Nicolas Schier <nicolas@...sle.eu> wrote:
>
> On Sat, 16 Jul 2022 18:31:22 +0900 Masahiro Yamada wrote:
> > Factor out the common prerequisites for DT compilation into the new
> > target, dtbs_prepare.
> >
> > Add comments in case you wonder why include/config/kernel.release is
> > the prerequisite. Our policy is that installation targets must not
> > (re)compile any build artifacts in the tree. If we make modules_install
> > depend on include/config/kernel.release and it is executed under the
> > root privilege, it may be owned by root.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> > ---
> >
> >  Makefile | 14 ++++++++++----
> >  1 file changed, 10 insertions(+), 4 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index a9bd55edb75e..8aa4dbb8f878 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -1367,16 +1367,22 @@ endif
> >
> >  ifneq ($(dtstree),)
> >
> > -%.dtb: include/config/kernel.release scripts_dtc
> > +%.dtb: dtbs_prepare
> >       $(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@
> >
> > -%.dtbo: include/config/kernel.release scripts_dtc
> > +%.dtbo: dtbs_prepare
> >       $(Q)$(MAKE) $(build)=$(dtstree) $(dtstree)/$@
>
> Is there a reason, why both rules are not unified?  I guess it is, but
> I can't see it.



See the GNU Make manual:
https://www.gnu.org/software/make/manual/html_node/Pattern-Examples.html

The last paragraph, "This pattern rule has two targets ..."



%.dtb %.dtbo: dtbs_prepare
         ...

means foo.dtb and foo.dtbo are generated at the same
time by the rule.  This is strange.





>
> >
> > -PHONY += dtbs dtbs_install dtbs_check
> > -dtbs: include/config/kernel.release scripts_dtc
> > +PHONY += dtbs dtbs_prepare dtbs_install dtbs_check
> > +dtbs: dtbs_prepare
> >       $(Q)$(MAKE) $(build)=$(dtstree)
> >
> > +# include/config/kernel.release is not actually required for building DTBs,
> > +# but for installing DTBs because INSTALL_DTBS_PATH contains $(KERNELRELEASE).
> > +# We do not want to move it to dtbs_install. The policy is installation
> > +# targets (, which may run as root) must not modify the tree.
>
> Is the comma after the opening parenthesis intended?


I will rephrase the comment in v2.




>
> Kind regards,
> Nicolas
>
> > +dtbs_prepare: include/config/kernel.release scripts_dtc
> > +
> >  ifneq ($(filter dtbs_check, $(MAKECMDGOALS)),)
> >  export CHECK_DTBS=y
> >  dtbs: dt_binding_check
> > --
> > 2.34.1



-- 
Best Regards
Masahiro Yamada