linux-kernel - Re: [PATCH v4] Kconfig: introduce HAS_IOPORT option and select it as necessary

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Message-ID: <B1EC1AC7-6BB5-4B66-B171-24687C3CBFB3@zytor.com>
Date:   Wed, 05 Apr 2023 13:00:27 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>,
        Arnd Bergmann <arnd@...db.de>,
        Richard Henderson <richard.henderson@...aro.org>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Geert Uytterhoeven <geert@...ux-m68k.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>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Yoshinori Sato <ysato@...rs.osdn.me>,
        Rich Felker <dalias@...c.org>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        "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
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-pci@...r.kernel.org, Arnd Bergmann <arnd@...nel.org>,
        Johannes Berg <johannes@...solutions.net>,
        linux-alpha@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-ia64@...r.kernel.org, loongarch@...ts.linux.dev,
        linux-m68k@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-riscv@...ts.infradead.org, linux-sh@...r.kernel.org,
        sparclinux@...r.kernel.org
Subject: Re: [PATCH v4] Kconfig: introduce HAS_IOPORT option and select it as necessary

On April 5, 2023 8:12:38 AM PDT, Niklas Schnelle <schnelle@...ux.ibm.com> wrote:
>On Thu, 2023-03-23 at 17:33 +0100, Niklas Schnelle wrote:
>> We introduce a new HAS_IOPORT Kconfig option to indicate 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 such as s390.
>> 
>> The following architectures do not select HAS_IOPORT:
>> 
>> * ARC
>> * C-SKY
>> * Hexagon
>> * Nios II
>> * OpenRISC
>> * s390
>> * User-Mode Linux
>> * Xtensa
>> 
>> All other architectures select HAS_IOPORT at least conditionally.
>> 
>> The "depends on" relations 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.
>> 
>> Co-developed-by: Arnd Bergmann <arnd@...nel.org>
>> Signed-off-by: Arnd Bergmann <arnd@...nel.org>
>> Acked-by: Johannes Berg <johannes@...solutions.net> # for ARCH=um
>> Acked-by: Geert Uytterhoeven <geert@...ux-m68k.org>
>> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
>> ---
>> Note: This patch is the initial patch of a larger series[0]. This patch
>> introduces the HAS_IOPORT config option while the rest of the series adds
>> driver dependencies and the final patch removes inb() / outb() and friends on
>> platforms that don't support them. 
>> 
>> Thus each of the per-subsystem patches is independent from each other but
>> depends on this patch while the final patch depends on the whole series. Thus
>> splitting this initial patch off allows the per-subsytem HAS_IOPORT dependency
>> addition be merged separately via different trees without breaking the build.
>> 
>> [0] https://lore.kernel.org/lkml/20230314121216.413434-1-schnelle@linux.ibm.com/
>> 
>> Changes since v3:
>> - List archs without HAS_IOPORT in commit message (Arnd)
>> - Select HAS_IOPORT for LoongArch (Arnd)
>> - Use "select HAS_IOPORT if (E)ISA || .." instead of a "depends on" for (E)ISA
>>   for m68k and parisc
>> - Select HAS_IOPORT with config GSC on parisc (Arnd)
>> - Drop "depends on HAS_IOPORT" for um's config ISA (Johannes)
>> - Drop "depends on HAS_IOPORT" for config ISA on x86 and parisc where it is
>>   always selected (Arnd)
>> 
>
>Gentle ping. As far as I can tell this hasn't been picked to any tree
>sp far but also hasn't seen complains so I'm wondering if I should send
>a new version of the combined series of this patch plus the added
>HAS_IOPORT dependencies per subsystem or wait until this is picked up.
>
>Thanks,
>Niklas
>
>

You need this on a system supporting not just ISA but also PCI.

Typically on non-x86 architectures this is simply mapped into a memory window.