[RFC v2 01/39] Kconfig: introduce HAS_IOPORT option and select it as necessary

[John Garry]

On 06/05/2022 10:38, Niklas Schnelle wrote:
> Another argument I see is that as shown by POWER9 we might start to see
> more platforms that just can't do I/O port access. E.g. I would also be
> surprised if Apple's M1 has I/O port access. Sooner or later I expect
> distributions on some platforms to only support such systems. For
> example on ppc a server distribution might only support IBM POWER
> without I/O port support before too long. Then having HAS_IOPORT allows
> to get rid of drivers that won't work anyway.
> 
> There are also reports of probing a driver with I/O ports causing a
> system crash on systems without I/O port support. For example in this
> answer by John Garry (added so he may supply more information):
> 
> https://lore.kernel.org/lkml/db043b76-880d-5fad-69cf-96abcd9cd34f@huawei.com/
> 
> .

That issue is that drivers like hwmon f71805f use inb/outb accessors 
with hardcoded IO port addresses to probe the driver. On archs like 
arm64 or powerpc - which do not natively support inb et al - this may 
crash the system when no PCI IO space is mapped [0]. Indeed, when PCI IO 
space is mapped, it is preferable these those drivers still would not 
access these ports.

So this series from Niklas could be used as a basis to solve that 
problem, in that we could also introduce something like HARDCODED_IOPORT 
[1] to stop those drivers being built at all for arm64.

[0] 
https://lore.kernel.org/linux-input/20210112055129.7840-1-song.bao.hua@hisilicon.com/T/#mf86445470160c44ac110e9d200b09245169dc5b6
[1] 
https://lore.kernel.org/lkml/CAK8P3a3HHeP+Gw_k2P7Qtig0OmErf0HN30G22+qHic_uZTh11Q@mail.gmail.com/

Thanks,
John