Re: `io{re,un}map()` build error in s390 under `!CONFIG_HAS_IOMEM`

Geert Uytterhoeven <[email protected]> Thu, 6 Aug 2026 17:21:24 +0200

Newsgroups	dev.linux.lists.driver-core,org.kernel.vger.linux-arch,org.kernel.vger.linux-s390,org.kernel.vger.rust-for-linux
Message-ID	<CAMuHMdWBiCA6+SWatmbB5bVdFd7_9CPNgR_eaTcOUpqAEA5J4w@mail.gmail.com>

Hi Arnd,

On Thu, 6 Aug 2026 at 15:51, Arnd Bergmann <[email protected]> wrote:
> I think the reason is that there are a couple of architectures
> (including non-MIO s390) that take a shortcut for normal
> ioremap() that avoids actually mapping anything, e.g. mips
> and related architectures have a fixed uncached mapping
> of all MMIO space visible to kernel, while some alpha, m68k
> powerpc, and s390 do something other than a pointer dereference
> for MMIO.

FTR, several m68k platforms use the transparent translation registers
to set up a mapping to the main system's MMIO space (like MIPS,
but programmable), and thus just need to add an offset.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds