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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Sat, 13 Mar 2021 21:10:37 +0900
Message-ID: <CAK7LNAT9n4OtyRHx+PyJi-1CoxHrRT8OV6nKuiqsnvSPO1jUeg@mail.gmail.com>
Subject: Re: [PATCH] xtensa: move CONFIG_CPU_*_ENDIAN defines to Kconfig
To:     Max Filippov <jcmvbkbc@gmail.com>
Cc:     Chris Zankel <chris@zankel.net>,
        "open list:TENSILICA XTENSA PORT (xtensa)" 
        <linux-xtensa@linux-xtensa.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Sat, Mar 13, 2021 at 9:03 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Sat, Mar 13, 2021 at 5:57 PM Max Filippov <jcmvbkbc@gmail.com> wrote:
> >
> > On Fri, Mar 12, 2021 at 7:14 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > >
> > > Move the definition of CONFIG_CPU_*_ENDIAN to Kconfig, the best place
> > > for CONFIG options.
> > >
> > > I slightly simplified the test code. You can use the -P option to suppress
> > > linemarker generation. The grep command is unneeded.
> > >
> > >   $ echo __XTENSA_EB__ | xtensa-linux-gcc -E -
> > >   # 1 "<stdin>"
> > >   # 1 "<built-in>"
> > >   # 1 "<command-line>"
> > >   # 1 "<stdin>"
> > >   1
> > >
> > >   $ echo __XTENSA_EB__ | xtensa-linux-gcc -E -P -
> > >   1
> > >
> > > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> > > ---
> >
> > > If I understood correctly, xtensa compilers can support either
> > > big-endian or little-endian. We cannot change it via a command option.
> > > Actually, it does not understand -mbig-endian or -mlittle-endian.
> > > (Is this correct?)
> >
> > This is correct. The idea is that specific xtensa core has fixed endianness,
> > but it can be either little or big. The toolchain is configured for the specific
> > xtensa core at build time, so there's no need for a runtime endian switch.
> >
> > >   $ xtensa-linux-gcc   -mbig-endian  /dev/null  -c -o /dev/null
> > >   xtensa-linux-gcc: error: unrecognized command-line option '-mbig-endian'
> > >
> > > I see -mbig-endian / -mlittle-endian in old GCC manual.
> > >   https://gcc.gnu.org/onlinedocs/gcc-3.3.5/gcc/Xtensa-Options.html
> > > But, I cannot see them in recent gcc manuals.
> > > So, I have no idea better than checking __XTENSA_EB__ or __XTENSA_EL__.
> > > I just moved the logic to Kconfig from Makefile.
> > >
> > >
> > >  arch/xtensa/Kconfig  | 6 ++++++
> > >  arch/xtensa/Makefile | 9 +--------
> > >  2 files changed, 7 insertions(+), 8 deletions(-)
> >
> > Acked-by: Max Filippov <jcmvbkbc@gmail.com>
> > Please let me know if I should take it into the xtensa tree or you will
> > carry it in the kbuild tree.
>
>
> Please apply it to the xtensa tree.
>

Ah, wait.

I think I can do a little more cleanups.

arch/xtensa/boot/Makefile:BIG_ENDIAN        := $(shell echo
__XTENSA_EB__ | $(CC) -E - | grep -v "\#")


Will send v2.

-- 
Best Regards
Masahiro Yamada