Re: [PATCH] arm: ioremap: Fix compilation of code which use pci_remap_iospace() without CONFIG_MMU

[Bjorn Helgaas]

On Thu, Jul 14, 2022 at 10:19:51PM +0200, Arnd Bergmann wrote:
> On Thu, Jul 14, 2022 at 8:57 PM Pali Rohár <pali@xxxxxxxxxx> wrote:
> > Custom ARM version of pci_remap_iospace() is implemented only for MMU
> > kernel builds. So do not define pci_remap_iospace() without CONFIG_MMU.
> >
> > See compilation failures:
> > https://lore.kernel.org/r/202112040150.wvyJZIZO-lkp@xxxxxxxxx/
> > https://lore.kernel.org/r/202112261802.u9iXqdWh-lkp@xxxxxxxxx/
> > https://lore.kernel.org/r/202201131529.A2s7rKQc-lkp@xxxxxxxxx/
> > https://lore.kernel.org/r/202203090147.24cUL0De-lkp@xxxxxxxxx/
> >
> > Fixes: bc02973a06a6 ("arm: ioremap: Implement standard PCI function pci_remap_iospace()")
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > Signed-off-by: Pali Rohár <pali@xxxxxxxxxx>
> >
> > ---
> >
> > PING!!!! Is somebody interested in fixing these compile errors? As nobody
> > answered to my emails where I proposed this fix more than half year ago and
> > asked for opinion...
> >
> > https://lore.kernel.org/r/20211204022131.bmhla4gkph7s7hy2@pali/
> > https://lore.kernel.org/r/20211205123209.lyx76daqdwzqwex4@pali/
> > https://lore.kernel.org/r/20211226215135.blcnafbuwhrq5ram@pali/
> > https://lore.kernel.org/r/20220113134938.3tx7iiukphvazvsq@pali/
> > https://lore.kernel.org/r/20220308184851.jmw2xvrapy5wzwof@pali/
> 
> Are you sure this still happens in mainline kernels? Since
> commit 2f618d5ef5dd ("ARM: remove support for NOMMU ARMv4/v5")
> it should no longer be possible to disable the MMU in any Arm machines
> other than the Cortex-M based ones, which do not support PCI.

I don't know whether it happens in mainline kernels either.

But even if the 2f618d5ef5dd Kconfiggery makes MMU mostly obsolete for
Arm, it seems a little weird that io.h unconditionally promises an
arch-specific implementation of pci_remap_iospace(), but we only
provide it when CONFIG_MMU=y.

It seems like it'd be a little cleaner if the same condition
determined visibility of both the declaration and the definition.

Bjorn