linux-kernel - Re: [PATCH v2 0/4] Regather scattered PCI-Code

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Message-Id: <3871b83a-0e80-402e-bbe6-359c17127842@app.fastmail.com>
Date:   Fri, 01 Dec 2023 17:27:40 +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>
Subject: Re: [PATCH v2 0/4] Regather scattered PCI-Code

On Fri, Dec 1, 2023, at 13:16, Philipp Stanner wrote:
>
> Arnd has suggested that architectures defining a custom inb() need their
> own iomem_is_ioport(), as well. I've grepped for inb() and found the
> following list of archs that define their own:
>   - alpha
>   - arm
>   - m68k <--
>   - parisc
>   - powerpc
>   - sh
>   - sparc
>   - x86 <--
>
> All of those have their own definitons of pci_iounmap(). Therefore, they
> don't need our generic version in the first place and, thus, also need
> no iomem_is_ioport().

What I meant of course is that they should define iomem_is_ioport()
in order to drop the custom pci_iounmap() and have only one remaining
definition of that function left.

The one special case that I missed the last time is s390, which
does not use GENERIC_PCI_IOMAP and will just require a separate
copy of pci_iounmap() to go along with the is custom pci_iomap().

> The two exceptions are x86 and m68k. The former uses lib/iomap.c through
> CONFIG_GENERIC_IOMAP, as Arnd pointed out in the previous discussion
> (thus, CONFIG_GENERIC_IOMAP is not really generic in this regard).
>
> So as I see it, only m68k WOULD need its own custom definition of
> iomem_is_ioport(). But as I understand it it doesn't because it uses the
> one from asm-generic/pci_iomap.h ??

At the moment, m68k gets the pci_iounmap() from lib/iomap.c
if PCI is enabled for coldfire, but that incorrectly calls
iounmap() on PCI_IO_PA if it gets passed a PIO address.

The version from asm-generic/io.h should fix this.

For classic m68k, there is no PCI, so nothing calls pci_iounmap().

> I wasn't entirely sure how to deal with the address ranges for the
> generic implementation in asm-generic/io.h. It's marked with a TODO.
> Input appreciated.

I commented on the function directly. To clarify, I think we should
be able to directly turn each pci_iounmap() definition into
a iomem_is_ioport() definition by keeping the logic unchanged
and just return 'true' for the PIO variant or 'false' for the MMIO
version.

> I removed the guard around define pci_iounmap in asm-generic/io.h. An
> alternative would be to have it be guarded by CONFIG_GENERIC_IOMAP and
> CONFIG_GENERIC_PCI_IOMAP, both. Without such a guard, there is no
> collision however, because generic pci_iounmap() from
> drivers/pci/iomap.c will only get pulled in when
> CONFIG_GENERIC_PCI_IOMAP is actually set.

The "#define pci_iomap" can be removed entirely I think.

     Arnd