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Date:   Wed, 05 Apr 2023 13:00:27 -0700
From:   "H. Peter Anvin" <hpa@zytor.com>
To:     Niklas Schnelle <schnelle@linux.ibm.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Richard Henderson <richard.henderson@linaro.org>,
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Subject: =?US-ASCII?Q?Re=3A_=5BPATCH_v4=5D_Kconfig=3A_introduce_HAS=5FI?= =?US-ASCII?Q?OPORT_option_and_select_it_as_necessary?=
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On April 5, 2023 8:12:38 AM PDT, Niklas Schnelle <schnelle@linux=2Eibm=2Eco=
m> 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=2E In a future patch HAS_IOPORT=3Dn will disable compilatio=
n of
>> the I/O accessor functions inb()/outb() and friends on architectures
>> which can not meaningfully support legacy I/O spaces such as s390=2E
>>=20
>> The following architectures do not select HAS_IOPORT:
>>=20
>> * ARC
>> * C-SKY
>> * Hexagon
>> * Nios II
>> * OpenRISC
>> * s390
>> * User-Mode Linux
>> * Xtensa
>>=20
>> All other architectures select HAS_IOPORT at least conditionally=2E
>>=20
>> 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=2E
>>=20
>> Co-developed-by: Arnd Bergmann <arnd@kernel=2Eorg>
>> Signed-off-by: Arnd Bergmann <arnd@kernel=2Eorg>
>> Acked-by: Johannes Berg <johannes@sipsolutions=2Enet> # for ARCH=3Dum
>> Acked-by: Geert Uytterhoeven <geert@linux-m68k=2Eorg>
>> Signed-off-by: Niklas Schnelle <schnelle@linux=2Eibm=2Ecom>
>> ---
>> Note: This patch is the initial patch of a larger series[0]=2E This pat=
ch
>> introduces the HAS_IOPORT config option while the rest of the series ad=
ds
>> driver dependencies and the final patch removes inb() / outb() and frie=
nds on
>> platforms that don't support them=2E=20
>>=20
>> Thus each of the per-subsystem patches is independent from each other b=
ut
>> depends on this patch while the final patch depends on the whole series=
=2E Thus
>> splitting this initial patch off allows the per-subsytem HAS_IOPORT dep=
endency
>> addition be merged separately via different trees without breaking the =
build=2E
>>=20
>> [0] https://lore=2Ekernel=2Eorg/lkml/20230314121216=2E413434-1-schnelle=
@linux=2Eibm=2Ecom/
>>=20
>> 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 || =2E=2E" 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 i=
t is
>>   always selected (Arnd)
>>=20
>
>Gentle ping=2E 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=2E
>
>Thanks,
>Niklas
>
>

You need this on a system supporting not just ISA but also PCI=2E

Typically on non-x86 architectures this is simply mapped into a memory win=
dow=2E