linux-kernel - Re: [GIT PULL 1/2] asm-generic: rework PCI I/O space access

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Date:   Tue, 3 Aug 2021 12:23:55 +0100
From:   John Garry <john.garry@...wei.com>
To:     Arnd Bergmann <arnd@...nel.org>
CC:     Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        Niklas Schnelle <schnelle@...ux.ibm.com>
Subject: Re: [GIT PULL 1/2] asm-generic: rework PCI I/O space access

>> Anyway, one thing I mentioned earlier was that we could solve the
>> problem of drivers accessing unmapped IO ports and crashing systems on
>> archs which define PCI_IOBASE by building them under some "native port
>> IO support" flag.
> Right, that was part of the goal here.

Great

> 
>> One example of such a driver was F71805F sensor. You put that under
>> HAS_IOPORT, which would be available for all archs, I think. But I could
>> not see where config LEGACY_PCI is introduced. Could we further refine
>> that config to not build for such archs as arm64?
>>
>> BTW, I think that the PPC dependency was added there to stop building
>> for power for that same reason, so hopefully we get rid of that.
> Good point. It seems that I actually never added the LEGACY_PCI option
> to my patch,

ok, it would be nice to see that.

> so I'm just not building those drivers any more, and not
> defining the inb()/outb() helpers either, causing a build failure when I'm
> missing an option.
> 
> However it sounds like you are interested in a third option here, which
> brings us to:
> 
> LEGACY_PCI: any PCI driver that uses inb()/outb() or is only available
>      on old-style PCI but not PCIe hardware without a bridge.
>      To be disabled for most architectures and possibly distros but can
>      be enabled for kernels that want to use those devices, as long as
>      CONFIG_HAS_IOPORT is set by the architecture.
> 
> HAS_IOPORT: not a legacy PCI device, but can only be built on
>      architectures that define inb()/outb(). To be disabled for s390
>      and any other machine that has no useful definition of those
>      functions.

That seems reasonable. And asm-generic io.h should be ifdef'ed by 
HAS_IOPORT. In your patch you had it under CONFIG_IOPORT - was that 
intentional?

On another point, I noticed SCSI driver AHA152x depends on ISA, but is 
not an isa driver - however it does use port IO. Would such dependencies 
need to be changed to depend on HAS_IOPORT?

I did notice that arm32 support CONFIG_ISA - not sure why.

> 
> HARDCODED_IOPORT: (or another name you might think of,) Used by
>     drivers that unconditionally do inb()/outb() without checking the
>     validity of the address using firmware or other methods first.
>     depends on HAS_IOPORT and possibly architecture specific
>     settings.

Yeah, that sounds the same as what I was thinking. Maybe IOPORT_NATIVE 
could work as a name. I would think that only x86/ia64 would define it. 
A concern though is that someone could argue that is a functional 
dependency, rather than just a build dependency.

Thanks,
John