Re: [PATCH v4] irq: add quirk for broken interrupt remapping on 55XX chipsets

[Bjorn Helgaas]

On Thu, Apr 4, 2013 at 2:04 PM, Neil Horman <nhorman@xxxxxxxxxxxxx> wrote:
> On Thu, Apr 04, 2013 at 10:40:07AM -0700, Yinghai Lu wrote:
>> On Thu, Apr 4, 2013 at 10:27 AM, Don Dutile <ddutile@xxxxxxxxxx> wrote:
>> >> You need to move the quirk to early_quirk to append nointremap to
>> >> avoid extra rebooting.
>> >>
>> > The pci-dev's of all the (minimally, root, 5500-chipset) pci-dev's are
>> > known/scanned/created by that time?
>>
>> in arch/x86/kernel/early-quirk.c
>>
>> and on top of
>> https://git.kernel.org/cgit/linux/kernel/git/yinghai/linux-yinghai.git/commit/?h=for-x86-early-quirk-usb&id=de38757e964cfee20e6da1977572a2191d7f4aa0
>>
>> You could add one entry in early_qrk[].
>>
>> Some one already try to use that path to disable x2apic on some thinkpad.
>>
>> So it should work on nointrremap too.
>>
> See my last email to Bjorn.  Doing this in early-quirks in such a way that we
> can detect an iommu that has interrupt remapping enabled (so we don't just
> unilaterally print this quirk all the time) requires that we be able to parse
> acpi tables very early in the boot.  If you know of how to do that, I can make
> this happen.  If not, I suppose another alternative would be to have the early
> quirk set a flag that tells us this is a bogus chip, and if we try to enable irq
> remapping with that flag set, we should fail, and report the error at that time,
> but I'm not sure I like that solution.

I like that solution :)  It seems very simple -- you don't have to
parse any tables or anything.

Bjorn
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