The issue here is the error handling within the ACPI layer.  gsi = 0 is a
valid return value from acpi_pci_irq_lookup, while gsi = (-1) is the value
returned when a PRT cannot be found.

This error in error handling can result in a WARN_ON at
arch/ia64/kernel/iosapic.c:622 .

The remaining fix is to complete error handling within the core IDE
layer and the IOC4 IDE driver.