Subject: Re: [GIT PULL 1/2] asm-generic: rework PCI I/O space access
To:     Niklas Schnelle <schnelle@linux.ibm.com>,
        Arnd Bergmann <arnd@kernel.org>
CC:     Linus Torvalds <torvalds@linux-foundation.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        linux-pci <linux-pci@vger.kernel.org>,
        "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>
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From:   John Garry <john.garry@huawei.com>
Message-ID: <53746e42-23a2-049d-9b38-dcfbaaae728f@huawei.com>
Date:   Fri, 17 Dec 2021 14:27:33 +0000
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On 17/12/2021 13:52, Niklas Schnelle wrote:

Thanks for looking at this again.

>>> I have tested this on s390 with HAS_IOPORT=n and allyesconfig as well
>>> as running it with defconfig. I've also been using it on my Ryzen 3990X
>>> workstation with LEGACY_PCI=n for a few days. I do get about 60 MiB
>>> fewer modules compared with a similar config of v5.15.8. Hard to say
>>> which other systems might miss things of course.
>>>
>>> I have not yet worked on the discussed IOPORT_NATIVE flag. Mostly I'm
>>> wondering two things. For one it feels like that could be a separate
>>> change on top since HAS_IOPORT + LEGACY_PCI is already quite big.
>>> Secondly I'm wondering about good ways of identifying such drivers and
>>> how much this overlaps with the ISA config flag.

I was interesting in the IOPORT_NATIVE flag (or whatever we call it) as 
it solves the problem of drivers which "unconditionally do inb()/outb() 
without checking the validity of the address using firmware or other 
methods first" being built for (and loaded on and crashing) unsuitable 
systems. Such a problem is in [0]

So if we want to support that later, then it seems that someone would 
need to go back and re-edit many same driver Kconfigs – like hwon, for 
example. I think it's better to avoid that and do it now.

Arnd, any opinion on that?

I'm happy to help with that effort.

[0] 
https://lore.kernel.org/lkml/1610729929-188490-1-git-send-email-john.garry@huawei.com/

Thanks,
John