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

From: John Garry <john.garry@huawei.com>
To: Niklas Schnelle <schnelle@linux.ibm.com>,
	Bjorn Helgaas <helgaas@kernel.org>,
	Arnd Bergmann <arnd@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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	Richard Henderson <rth@twiddle.net>,
	Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
	Matt Turner <mattst88@gmail.com>,
	Russell King <linux@armlinux.org.uk>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Michal Simek <monstr@monstr.eu>,
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Subject: Re: [RFC v2 01/39] Kconfig: introduce HAS_IOPORT option and select it as necessary
Date: Fri, 6 May 2022 12:07:26 +0100	[thread overview]
Message-ID: <7b8d7c1a-58c3-4ba9-a4f0-d0e051f3ffdc@huawei.com> (raw)
In-Reply-To: <157602011a72061dd31f92bd699e8c1f9a81c988.camel@linux.ibm.com>

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