linux-kernel - Re: [PATCH v2 4/4] lib, pci: unify generic pci

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Date:   Fri, 01 Dec 2023 22:32:22 +0100
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Philipp Stanner" <pstanner@...hat.com>,
        "Bjorn Helgaas" <bhelgaas@...gle.com>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "Dan Williams" <dan.j.williams@...el.com>,
        "Jonathan Cameron" <Jonathan.Cameron@...wei.com>,
        "Jakub Kicinski" <kuba@...nel.org>,
        "Dave Jiang" <dave.jiang@...el.com>,
        "Uladzislau Koshchanka" <koshchanka@...il.com>,
        "Neil Brown" <neilb@...e.de>,
        "Niklas Schnelle" <schnelle@...ux.ibm.com>,
        "John Sanpe" <sanpeqf@...il.com>,
        "Kent Overstreet" <kent.overstreet@...il.com>,
        "Masami Hiramatsu" <mhiramat@...nel.org>,
        "Kees Cook" <keescook@...omium.org>,
        "David Gow" <davidgow@...gle.com>,
        "Yury Norov" <yury.norov@...il.com>,
        "wuqiang.matt" <wuqiang.matt@...edance.com>,
        "Jason Baron" <jbaron@...mai.com>,
        "Kefeng Wang" <wangkefeng.wang@...wei.com>,
        "Ben Dooks" <ben.dooks@...ethink.co.uk>,
        "Danilo Krummrich" <dakr@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        Linux-Arch <linux-arch@...r.kernel.org>,
        "Arnd Bergmann" <arnd@...nel.org>
Subject: Re: [PATCH v2 4/4] lib, pci: unify generic pci_iounmap()

On Fri, Dec 1, 2023, at 20:37, Philipp Stanner wrote:
> On Fri, 2023-12-01 at 16:26 +0100, Arnd Bergmann wrote:
>> 
>> static inline bool struct iomem_is_ioport(void __iomem *p)
>> {
>> #ifdef CONFIG_HAS_IOPORT
>>         uintptr_t start = (uintptr_t) PCI_IOBASE;
>>         uintptr_t addr = (uintptr_t) p;
>> 
>>         if (addr >= start && addr < start + IO_SPACE_LIMIT)
>>                 return true;
>> #endif
>>         return false;
>> }
>> 
>> > +#else /* CONFIG_GENERIC_IOMAP. Version from lib/iomap.c will be
>> > used. 
>> > */
>> > +bool iomem_is_ioport(void __iomem *addr);
>> > +#define ARCH_WANTS_GENERIC_IOMEM_IS_IOPORT
>> 
>> I'm not sure what this macro is for, since it appears to
>> do the opposite of what its name suggests: rather than
>> provide the generic version of iomem_is_ioport(), it
>> skips that and provides a custom one to go with lib/iomap.c
>
> Hmmm well now it's getting tricky.
>
> This else-branch is the one where CONFIG_GENERIC_IOMAP is actually set.
>
> I think we're running into the "generic not being generic now that IA64
> has died" problem you were hinting at.
>
> If we build for x86 and have CONFIG_GENERIC set, only then do we want
> iomem_is_ioport() from lib/iomap.c. So the macro serves avoiding a
> collision between symbols. Because lib/iomap.c might be compiled even
> if someone else already has defined iomem_is_ioport().
> I also don't like it, but it was the least bad solution I could come up
> with
> Suggestions?

The best I can think of is to move the lib/iomap.c version
of iomem_is_ioport() to include/asm-generic/iomap.h with
an #ifndef iomem_is_ioport / #define iomem_is_ioport
check around it. This file is only included on parisc, alpha,
sh and when CONFIG_GENERIC_IOMAP is set.

The default version in asm-generic/io.h then just needs
one more #ifdef iomem_is_ioport check around it.

      Arnd