linux-kernel - Re: [RFC PULL] remove arch/h8300

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Date:   Mon, 4 Apr 2022 13:48:15 -0700
From:   Max Filippov <jcmvbkbc@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        "moderated list:H8/300 ARCHITECTURE" 
        <uclinux-h8-devel@...ts.sourceforge.jp>,
        "open list:TENSILICA XTENSA PORT (xtensa)" 
        <linux-xtensa@...ux-xtensa.org>,
        Linux-sh list <linux-sh@...r.kernel.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Damien Le Moal <damien.lemoal@....com>,
        linux-riscv <linux-riscv@...ts.infradead.org>
Subject: Re: [RFC PULL] remove arch/h8300

On Mon, Apr 4, 2022 at 12:36 PM Arnd Bergmann <arnd@...db.de> wrote:
> On Mon, Apr 4, 2022 at 9:14 PM Max Filippov <jcmvbkbc@...il.com> wrote:
> > On Mon, Apr 4, 2022 at 12:01 PM Arnd Bergmann <arnd@...db.de> wrote:
> > > On Mon, Apr 4, 2022 at 7:57 PM Max Filippov <jcmvbkbc@...il.com> wrote:
> > > > Please let me know if you observe any specific build/runtime issues.
> > > xtensa-linux-gcc-11.1.0 -DKCONFIG_SEED=
> > ...
> > > /git/arm-soc/arch/xtensa/kernel/head.S: Assembler messages:
> > > /git/arm-soc/arch/xtensa/kernel/head.S:87: Error: invalid register
> > > 'atomctl' for 'wsr' instruction
> >
> > Sure, one cannot use an arbitrary xtensa compiler for the kernel
> > build, the compiler configuration must match the core variant selected
> > in the linux configuration. Specifically, for the nommu_kc705_defconfig
> > the following compiler can be used:
> >
> > https://github.com/foss-xtensa/toolchain/releases/download/2020.07/x86_64-2020.07-xtensa-de212-elf.tar.gz
> >
> > If you build the toolchain yourself using crosstool-ng or buildroot they
> > accept the 'configuration overlay' parameter that does the compiler
> > customization.
> >
> > Perhaps the documentation for this part is what needs to be improved.
>
> It sounds like a bug in the kernel Makefile. On all other architectures,
> you can generally just pick any (recent) compiler and build any kernel,
> as the compiler arguments set the exact target machine type based
> on the kernel config. You can't normally rely on the compiler defaults
> for kernel builds.

It's not just the defaults. The binary instruction encoding is configurable
on the xtensa architecture, configuration overlay replaces parts of
the toolchain that do that.
The additional CPU state is configurable and the kernel gets customized
with the code that loads and stores this state when someone builds it for
a specific xtensa core.
These customizations are done by the users of the xtensa architecture and
there are hundreds of configurations in existence. The toolchain has never
been supposed to support all of them at once.

-- 
Thanks.
-- Max