Architecture dependent IRQ resources such as interrupt vector for PCI
devices are allocated at pci_enable_device() time on i386, x86-64 and
ia64 platform. Today, however, these IRQ resources are never
deallocated even if they are no longer used. The following set of
patches adds supports to deallocate IRQ resources at
pci_disable_device() time.

The motivation of the set of patches is as follows:

    - IRQ resources such as interrupt vectors should be freed if they
      are no longer used because the amount of these resources are
      limited. By deallocating IRQ resources, we can recycle them.

    - I think some hardwares will support hot-pluggable I/O units with
      I/O xAPICs in the near future. So I/O xAPIC hot-plug support by
      OS will be needed soon. IRQ resouces deallocation will be one of
      the most important stuff for I/O xAPIC hot-plug.

For now, the following set of patches has ia64 implementation only.
i386 and x86_64 implementations are TBD.




This patch is ACPI portion of IRQ deallocation. This patch defines the
following new interface. The implementation of this interface depends
on each platform.

    o void acpi_unregister_gsi(u32 gsi)

        This is a opposite portion of acpi_register_gsi(). This has a
        responsibility for deallocating IRQ resources associated with
        the specified GSI number.

        We need to consider the case of shared interrupt. In the case
        of shared interrupt, acpi_register_gsi() is called multiple
        times for one gsi. That is, registrations and unregistrations
        can be nested.

        This function undoes the effect of one call to
        acpi_register_gsi(). If this matches the last registration,
        IRQ resources associated with the specified GSI number are
        freed.

This patch also adds the following new function.

    o void acpi_pci_irq_disable (struct pci_dev *dev)

        This function is a opposite portion of
        acpi_pci_enable_irq(). It clears the device's linux IRQ number
        and calls acpi_unregister_gsi() to deallocate IRQ resources.
Signed-off-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>