linux-kernel - Re: [RFC 02/32] Kconfig: introduce HAS_IOPORT option and select it as necessary

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Message-ID: <CAMuHMdXk6VcDryekkMJ3aGFnw4LLWOWMi8M2PwjT81PsOsOBMQ@mail.gmail.com>
Date:   Tue, 28 Dec 2021 11:08:05 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        John Garry <john.garry@...wei.com>,
        Nick Hu <nickhu@...estech.com>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>, Guo Ren <guoren@...nel.org>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Chris Zankel <chris@...kel.net>,
        Karol Gugala <kgugala@...micro.com>,
        Jeff Dike <jdike@...toit.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Brian Cain <bcain@...eaurora.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Vineet Gupta <vgupta@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Michal Simek <monstr@...str.eu>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
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        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-csky@...r.kernel.org,
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        Michael Schmitz <schmitzmic@...il.com>,
        Greg Ungerer <gerg@...ux-m68k.org>
Subject: Re: [RFC 02/32] Kconfig: introduce HAS_IOPORT option and select it as necessary

Hi Niklas,

On Mon, Dec 27, 2021 at 5:44 PM Niklas Schnelle <schnelle@...ux.ibm.com> wrote:
> We introduce a new HAS_IOPORT Kconfig option to gate support for
> I/O port access. In a future patch HAS_IOPORT=n will disable compilation
> of the I/O accessor functions inb()/outb() and friends on architectures
> which can not meaningfully support legacy I/O spaces. On these platforms
> inb()/outb() etc are currently just stubs in asm-generic/io.h which when
> called will cause a NULL pointer access which some compilers actually
> detect and warn about.
>
> The dependencies on HAS_IOPORT in drivers as well as ifdefs for
> HAS_IOPORT specific sections will be added in subsequent patches on
> a per subsystem basis. Then a final patch will ifdef the I/O access
> functions on HAS_IOPORT thus turning any use not gated by HAS_IOPORT
> into a compile-time warning.
>
> Link: https://lore.kernel.org/lkml/CAHk-=wg80je=K7madF4e7WrRNp37e3qh6y10Svhdc7O8SZ_-8g@mail.gmail.com/
> Co-developed-by: Arnd Bergmann <arnd@...nel.org>
> Signed-off-by: Arnd Bergmann <arnd@...nel.org>
> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>

Thanks for your patch!

> --- a/arch/m68k/Kconfig
> +++ b/arch/m68k/Kconfig
> @@ -16,6 +16,7 @@ config M68K
>         select GENERIC_CPU_DEVICES
>         select GENERIC_IOMAP
>         select GENERIC_IRQ_SHOW
> +       select HAS_IOPORT
>         select HAVE_AOUT if MMU
>         select HAVE_ASM_MODVERSIONS
>         select HAVE_DEBUG_BUGVERBOSE

This looks way too broad to me: most m68k platform do not have I/O
port access support.

My gut feeling says:

    select HAS_IOPORT if PCI || ISA

but that might miss some intricate details...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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