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

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Message-ID: <65079f6d5f512f9aff003bdfea127b214a9f9290.camel@redhat.com>
Date:   Fri, 01 Dec 2023 20:09:51 +0100
From:   Philipp Stanner <pstanner@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>, 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>, pstanner@...hat.com
Subject: Re: [PATCH v2 0/4] Regather scattered PCI-Code

On Fri, 2023-12-01 at 17:27 +0100, Arnd Bergmann wrote:
> 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.

Ah, gotcha!
Yes, that would be neat. Would also allow for droping
ARCH_WANTS_GENERIC_PCI_IOUNMAP.

> 
> 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.

So, to be sure: m68k will use the generic iomem_is_ioport() despite
defining its own inb()?

> 
> 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.

I also think it can, because first arch/asm/io.h includes asm-
generic/io.h.
I was just wondering why many other functions in asm-generic/io.h
always define their own names..

It's obviously very hard to test which config will break, so I thought
it's better safe than sorry here

P.

> 
>      Arnd
>