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

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Date:   Wed, 4 Aug 2021 08:55:38 +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

On 03/08/2021 13:15, Arnd Bergmann wrote:
>> 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?
> No, that was a typo. Thanks for pointing this out.
> 
>> 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'm not sure what you mean here. As far as I can tell, AHA152x is an ISA
> driver in the sense that it is a driver for ISA add-on cards. However, it
> is not a 'struct isa_driver' in the sense that AHA1542 is, AHA152x  is even
> older and uses the linux-2.4 style initialization using a module_init()
> function that does the probing.

ok, fine. So I just wonder what the ISA kconfig dependency gets us for 
aha152x. I experimented by removing the kconfig dependency and enabling 
for the arm64 (which does not have CONFIG_ISA) std defconfig and it 
built fine.

> 
>> I did notice that arm32 support CONFIG_ISA - not sure why.
> This is for some of the earlier machines we support:
> mach-footbridge has some on-board ISA components, while
> SA1100, PXA25x and S3C2410 each have at least one machine
> with a PC/104 connector using ISA signaling for add-on cards.
> 
> There are also a couple of platforms with PCMCIA or CF slots
> using the same ISA style I/O signals, but those have separate
> drivers.
> 
>>> 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.
> You can have those on a number of platforms, such as early
> PowerPC CHRP or pSeries systems, a number of MIPS workstations
> including recent Loongson machines, and many Alpha platforms.
> 

hmmm... if some machines under an arch support "native" port IO and some 
don't, then if we use a common multi-platform defconfig which defines 
HARDCODED_IOPORT, then we still build for platforms without "native" 
port IO, which is not ideal.

> Maybe the name should reflect that these all use PC-style ISA/LPC
> port numbers without the ISA connectors.

Thanks,
john