linux-kernel - Re: [PATCH] x86: fix PCI

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Date:	Fri, 4 Oct 2013 11:36:33 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Lior Amsalem <alior@...vell.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	daniel.price@...il.com, Thierry Reding <thierry.reding@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jason Cooper <jason@...edaemon.net>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH] x86: fix PCI_MSI build on !SMP

[+cc Konrad]

On Thu, Oct 3, 2013 at 3:59 AM, Thomas Petazzoni
<thomas.petazzoni@...e-electrons.com> wrote:
> Commit ebd97be635 ('PCI: remove ARCH_SUPPORTS_MSI kconfig option')
> removed the ARCH_SUPPORTS_MSI option which architectures could select
> to indicate that they support MSI. Now, all architectures are supposed
> to build fine when MSI support is enabled: instead of having the
> architecture tell *when* MSI support can be used, it's up to the
> architecture code to ensure that MSI support can be enabled.
>
> On x86, commit ebd97be635 removed the following line:
>
>   select ARCH_SUPPORTS_MSI if (X86_LOCAL_APIC && X86_IO_APIC)
>
> Which meant that MSI support was only available when the local APIC
> and I/O APIC were enabled. While this is always true on SMP or x86-64,
> it is not necessarily the case on i386 !SMP.
>
> The below patch makes sure that the local APIC and I/O APIC support is
> always enabled when MSI support is enabled. To do so, it:
>
>  * Ensures the X86_UP_APIC option is not visible when PCI_MSI is
>    enabled. This is the option that allows, on UP machines, to enable
>    or not the APIC support. It is already not visible on SMP systems,
>    or x86-64 systems, for example. We're simply also making it
>    invisible on i386 MSI systems.
>
>  * Ensures that the X86_LOCAL_APIC and X86_IO_APIC options are 'y'
>    when PCI_MSI is enabled.
>
> Notice that this change requires a change in drivers/iommu/Kconfig to
> avoid a recursive Kconfig dependencey. The AMD_IOMMU option selects
> PCI_MSI, but was depending on X86_IO_APIC. This dependency is no
> longer needed: as soon as PCI_MSI is selected, the presence of
> X86_IO_APIC is guaranteed. Moreover, the AMD_IOMMU already depended on
> X86_64, which already guaranteed that X86_IO_APIC was enabled, so this
> dependency was anyway redundant.
>
> Signed-off-by: Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
> Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Cc: bhelgaas@...gle.com
> Cc: benh@...nel.crashing.org
> Cc: daniel.price@...il.com
> Cc: thierry.reding@...il.com
> Cc: linux-kernel@...r.kernel.org
> Cc: jason@...edaemon.net
> Cc: x86@...nel.org

FWIW,

Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>

x86 maintainers, I assume you'll pick this up.  Let me know if you
want me to do it.

Bjorn
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