On Fri, Dec 17, 2021 at 2:19 PM Niklas Schnelle [off-list ref] 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.

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