linux-kernel - Re: [PATCH] pci: Add dummy for pci_acs_enabled() if CONFIG

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Date:   Fri, 22 Sep 2017 20:12:46 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, Arnd Bergmann <arnd@...db.de>,
        Alex Williamson <alex.williamson@...hat.com>,
        Joerg Roedel <jroedel@...e.de>,
        linux-pci <linux-pci@...r.kernel.org>,
        iommu@...ts.linux-foundation.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pci: Add dummy for pci_acs_enabled() if CONFIG_PCI=n to
 fix iommmu build

Hi Björn,

On Fri, Sep 22, 2017 at 5:56 PM, Bjorn Helgaas <helgaas@...nel.org> wrote:
> On Mon, Sep 11, 2017 at 02:29:15PM +0200, Geert Uytterhoeven wrote:
>> If CONFIG_PCI=n, and gcc (e.g. 4.1.2) decides not to inline
>> get_pci_function_alias_group(), the build fails with:
>>
>>     drivers/iommu/iommu.o: In function `get_pci_function_alias_group':
>>     iommu.c:(.text+0xfdc): undefined reference to `pci_acs_enabled'
>>
>> Due to the various dummies for PCI calls in the CONFIG_PCI=n case,
>> pci_acs_enabled() isn't actually ever called, but not all versions of
>> gcc are smart enough to realize that.
>>
>> While explicitly marking get_pci_function_alias_group() inline would fix
>> the build, this would inflate the code for the CONFIG_PCI=y case, as
>> get_pci_function_alias_group() is a not-so-small function called from
>> two places.
>>
>> Hence fix the issue by introducing a dummy for pci_acs_enabled()
>> instead.
>>
>> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
>
> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
>
> Joerg, if you pick this up, would you mind capitalizing the subject
> line to match the PCI convention, e.g.,
>
>   PCI: Add dummy pci_acs_enabled() for CONFIG_PCI=n build
>
> If it's too late for you to pick this up this week, I can include it
> next week.  I assume this is not related to a specific change, i.e.,
> it's not a regression?  Should it be marked for stable?

It was introduced by commit 0ae349a0f33fb040 ("iommu/qcom: Add qcom_iommu"),
which enabled IOMMU support for compile-testing in e.g. allmodconfig on
platforms that don't have IOMMUs.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds