Commit ebd97be6 ('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 ebd97be6 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@free-electrons.com>
Link: http://lkml.kernel.org/r/1380794354-9079-1-git-send-email-thomas.petazzoni@free-electrons.comReported-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>