Subject: Re: [GIT PULL 1/2] asm-generic: rework PCI I/O space access
To:     Arnd Bergmann <arnd@kernel.org>
CC:     Niklas Schnelle <schnelle@linux.ibm.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        linux-pci <linux-pci@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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From:   John Garry <john.garry@huawei.com>
Message-ID: <cd9310ab-6012-a410-2bfc-a2f8dd8d62f9@huawei.com>
Date:   Fri, 17 Dec 2021 15:27:09 +0000
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On 17/12/2021 14:32, Arnd Bergmann wrote:
>> I was interesting in the IOPORT_NATIVE flag (or whatever we call it) as
>> it solves the problem of drivers which "unconditionally do inb()/outb()
>> without checking the validity of the address using firmware or other
>> methods first" being built for (and loaded on and crashing) unsuitable
>> systems. Such a problem is in [0]
>>
>> So if we want to support that later, then it seems that someone would
>> need to go back and re-edit many same driver Kconfigs – like hwmon, for
>> example. I think it's better to avoid that and do it now.
>>
>> Arnd, any opinion on that?
>>
>> I'm happy to help with that effort.
> I looked at the options the other day and couldn't really find any that
> fell into this category, so I suggested that Niklas would skip that for the
> moment. 

 From looking at the patch Niklas directed us at, as I understand, 
HAS_IOPORT is to decide whether the arch/platform may support PIO 
accessors - inb et al. And on that basis I am confused why it is not 
selected for arm64. And further compounded by:

  config INDIRECT_PIO
	 	bool "Access I/O in non-MMIO mode"
	 	depends on ARM64
	+	depends on HAS_IOPORT

If arm64 does not select, then why depend on it?

 > If you have a better way of finding the affected drivers,
 > that would be great.

Assuming arm64 should select HAS_IOPORT, I am talking about f71805f as 
an example. According to that patch, this driver additionally depends on 
HAS_IOPORT; however I would rather arm64, like powerpc, should not allow 
that driver to be built at all.

Thanks,
John