linux-kernel - Re: [RFC 00/32] Kconfig: Introduce HAS_IOPORT and LEGACY

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Message-ID: <38c595ea-f2fb-db54-397b-41c67fa59208@huawei.com>
Date:   Fri, 7 Jan 2022 16:57:44 +0000
From:   John Garry <john.garry@...wei.com>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>,
        Arnd Bergmann <arnd@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Nick Hu <nickhu@...estech.com>,
        Greentime Hu <green.hu@...il.com>,
        Vincent Chen <deanbo422@...il.com>,
        "Paul Walmsley" <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>, Guo Ren <guoren@...nel.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-arch@...r.kernel.org>,
        <linux-pci@...r.kernel.org>, <linux-riscv@...ts.infradead.org>,
        <linux-csky@...r.kernel.org>
Subject: Re: [RFC 00/32] Kconfig: Introduce HAS_IOPORT and LEGACY_PCI options

On 07/01/2022 07:21, Niklas Schnelle wrote:
> I checked again by adding
> 
> config HAS_IOPORT
>         def_bool n
> 
> in arch/s390/Kconfig and that doesn't seem to make a difference,
> allyesconfig builds all the same. Also checked for CONFIG_HAS_IOPORT in
> my .config and that isn't listed with or without the above addition.

Strange, as I build your branch and I see it:

HEAD is now at 9f421b6580ed asm-generic/io.h: drop inb() etc for 
HAS_IOPORT=n
john@...alhost:~/kernel-dev5> export ARCH=s390
john@...alhost:~/kernel-dev5> export 
CROSS_COMPILE=/usr/bin/s390x-suse-linux-
john@...alhost:~/kernel-dev5> make allyesconfig
#
# configuration written to .config
#
john@...alhost:~/kernel-dev5> more .config | grep HAS_IOPORT
CONFIG_HAS_IOPORT=y

> 
> I think this is because without a help text there is no "config
> question" and thus nothing that allyesconfig would set to yes. I do
> agree though that it's better to be explicit and add the above to those
> Kconfigs that don't support HAS_IOPORT.

So maybe something like:
config HAS_IOPORT
	def_bool ISA || LEGACY_PCI
	depends on !S390

Otherwise you can build inb et al from asm-generic/io.h and get the 
original compile error about arithmetic on NULL pointer, right?

But I assume that there is a more elegant way of doing this...

Thanks,
John