linux-kernel - Re: [GIT PULL 1/2] asm-generic: rework PCI I/O space access

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Message-ID: <849d70bddde1cfcb3ab1163970a148ff447ee94b.camel@linux.ibm.com>
Date:   Fri, 17 Dec 2021 14:52:05 +0100
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     John Garry <john.garry@...wei.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL 1/2] asm-generic: rework PCI I/O space access

On Fri, 2021-12-17 at 14:32 +0100, Arnd Bergmann wrote:
> On Fri, Dec 17, 2021 at 2:19 PM Niklas Schnelle <schnelle@...ux.ibm.com> wrote:
> > I've had some time to look into this a bit. As a refreshed starting
> > point I have rebased Arnd's patch to v5.16-rc5. Since I'm not sure how
> > to handle authorship and it's very early I haven't sent it as RFC but
> > it's available as a patch from my GitHub here:
> > https://gist.github.com/niklas88/a08fe76bdf9f5798500fccea6583e275
> > 
> > I have incorporated the following findings from this thread already:
> > 
> > - Added HAS_IOPORT to arch Kconfigs
> > - Added "config LEGACY_PCI" to drivers/pci/Kconfig
> > - Fixed CONFIG_HAS_IOPORT typo in asm-generic/io.h
> > - Removed LEGACY_PCI dependency of i2c-i801.
> >   Which is also used in current gen Intel platforms
> >   and depends on x86 anyway.
> > 
> > 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'd of course appreciate feedback. If you agree this is still
> > worthwhile to persue I'd think the next step would be trying to
> > refactor this into more manageable patches.
> 
> Thanks a lot for restarting this work! I think this all looks reasonable
> (a lot was my original patch anyway, so of course I think that ;)), but
> it would be good to split it up into multiple patches.

Yes definitely.

> 
> The CONFIG_LEGACY_PCI should take care of a lot of it, and I
> think that can be a single patch. I'd expand the Kconfig description
> to explain that this also covers PCIe devices that use the legacy
> I/O space even if they do not have a PCIe-to-PCI bridge in them.
> 
> The introduction of CONFIG_HAS_IOPORT, plus selecting it from
> the respective architectures makes sense as another patch, but
> I would make that separate from the #ifdef and 'depends on'
> changes to individual subsystems or drivers, as they are
> better reviewed separately.
> 
>         Arnd

Sounds like a plan. How should I mark authorship in the split up
patches. I definitely still see you as the main author to all of this
but of course I'll have to do quite a bit of editing and you shouldn't
get blamed for any mistakes I make. So not sure how to handle Sign-off-
bys and git's author property.