RE: ACPI: PCI Interrupt Link [LNKA] (IRQs *7)

["Brown, Len" <len.brown@intel.com>]

> ACPI: PCI Interrupt Link [LNKG](IRQs 3 4 5 6 7 10 11 12 14 15) *0, disabled.
> ACPI: PCI Interrupt Link [LNKH](IRQs 3 4 5 6 7 *10 11 12 14 15)

ACPI PCI Interrupt Links are a way to connect device interrupt
wires to (an assortment of) interrupt controller IRQ inputs.

The "disabled" simply means that particular link
isn't being used -- likely because the link is used
only in another mode (eg. PIC vs APIC mode), or because
there is nothing attached to that interrupt wire.

The kernel will complain loudly if a device references
a disabled link, as it would be a BIOS bug.

The '*' is the IRQ that the link is currently using.

Later on in the dmesg you will be able to see
at device probe time which links are used by
which devices.

In PIC mode we don't balance the IRQs between
links -- though you could enable it with "acpi_irq_balance".
The reason we don't is because too many legacy BIOSs
fail when we do.

In IOAPIC mode, acpi_irq_balance is enabled by default.

This process assigns devices to IRQs, and the idea of
'balance' here is to minimize sharing of the same IRQ
wire between multiple devices.

This has nothing to do with the run-time balancing
to target a given IRQ at a specific CPU.

cheers,
-Len
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