linux-kernel - Re: [PATCH 17/17] arm64: Do not expose PCI mmap through procfs

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Date:   Fri, 24 Mar 2017 16:20:46 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     linux-pci <linux-pci@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 17/17] arm64: Do not expose PCI mmap through procfs

On Fri, 2017-03-24 at 17:13 +0100, Arnd Bergmann wrote:
> 
> I'd still prefer this to be a whitelist of the existing architectures using PCI
> MMAP in procfs, there is really no reason for arm64 to be special, the
> one thing we want to control here is whether new architectures (including
> arm64) that have never had either the sysfs or the procfs interface
> should get one or both of them.
>
> As it seems that there are important use cases for the sysfs interface
> and your patch series will just make that work everywhere, I'd argue
> that we should just always provide the sysfs interface now, and use
> HAVE_PCI_MMAP only control the procfs interface.

I still have no sympathy for the "we don't want <this> tiny part of the
legacy generic non-architecture-specific procfs ABI to exist on ARM64".
Why not just kill /proc/bus/pci *entirely* there?

But sure, I suppose we could refactor things so that the sysfs mmap
bits depend on (HAVE_PCI_MMAP || ARCH_GENERIC_MMAP_RESOURCE_RANGE)
rather than having architectures define the latter in *addition* to the
former.

> That way, we turn on the sysfs interface on arc, arm64, frv and tile
> as well as any future architecture with PCI support, but leave
> the procfs support as opt-in.

OK. My plan was for ARCH_GENERIC_MMAP_RESOURCE_RANGE to go away once
all architectures were converted, and HAVE_PCI_MMAP to be all that's
left. It does make send to do arc, fr-v and tile too though. So we can
do it that way.
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