When parsing PnP ACPI resource structures, it may happen that some of
the resources are disabled (in which case "the size" of the resource
equals zero).

The current solution is to skip these resources completely - with the
unfortunate side effect that they are not registered despite the fact
that they exist, after all.  (The downside of this approach is that
these resources cannot be used as templates for setting the actual
device's resources because they are missing from the template.) The
kernel's APM implementation does not suffer from this problem and
registers all resources regardless of "their size".

This patch fixes a problem with (at least) the vintage IBM ThinkPad 600E
(and most likely also with the 600, 600X, and 770X which have a very
similar layout) where some of its PnP devices support options where
either an IRQ, a DMA, or an IO port is disabled.  Without this patch,
the devices can not be configured using the
"/sys/bus/pnp/devices/*/resources" interface.

The manipulation of these resources is important because the 600E has
very demanding requirements.  For instance, the number of IRQs is not
sufficient to support all devices of the 600E.  Fortunately, some of the
devices, like the sound card's MPU-401 UART, can be configured to not
use any IRQ, hence freeing an IRQ for a device that requires one.
(Still, the device's "ResourceTemplate" requires an IRQ resource
descriptor which cannot be created if the resource has not been
registered in the first place.)

As an example, the dependent sets of the 600E's CSC0103 device (the
MPU-401 UART) are listed, with the patch applied, as:

  Dependent: 00 - Priority preferred
    port 0x300-0x330, align 0xf, size 0x4, 16-bit address decoding
    irq <none> High-Edge
  Dependent: 01 - Priority acceptable
    port 0x300-0x330, align 0xf, size 0x4, 16-bit address decoding
    irq 5,7,2/9,10,11,15 High-Edge

(The same result is obtained when PNPBIOS is used instead of PnP ACPI.)
Without the patch, the IRQ resource in the preferred option is not
listed at all:

  Dependent: 00 - Priority preferred
    port 0x300-0x330, align 0xf, size 0x4, 16-bit address decoding
  Dependent: 01 - Priority acceptable
    port 0x300-0x330, align 0xf, size 0x4, 16-bit address decoding
    irq 5,7,2/9,10,11,15 High-Edge

And in fact, the 600E's DSDT lists the disabled IRQ as an option, as can
be seen from the following excerpt from the DSDT:

	Name (_PRS, ResourceTemplate ()
	{
        StartDependentFn (0x00, 0x00)
        {
            IO (Decode16, 0x0300, 0x0330, 0x10, 0x04)
            IRQNoFlags () {}
        }
        StartDependentFn (0x01, 0x00)
        {
            IO (Decode16, 0x0300, 0x0330, 0x10, 0x04)
            IRQNoFlags () {5,7,9,10,11,15}
        }
        EndDependentFn ()
	})

With this patch applied, a user space program - or maybe even the kernel
- can allocate all devices' resources optimally.  For the 600E, this
means to find optimal resources for (at least) the serial port, the
parallel port, the infrared port, the MWAVE modem, the sound card, and
the MPU-401 UART.

The patch applies the idea to register disabled resources to all types
of resources, not just to IRQs, DMAs, and IO ports.  At the same time,
it mimics the behavior of the "pnp_assign_xxx" functions from
"drivers/pnp/manager.c" where resources with "no size" are considered
disabled.

No regressions were observed on hardware that does not require this
patch.

The patch is applied against 2.6.39.

NB: The kernel's current PnP interface does not allow for disabling individual
resources using the "/sys/bus/pnp/devices/$device/resources" file.  Assuming
this could be done, a device could be configured to use a disabled resource
using a simple series of calls:

  echo disable > /sys/bus/pnp/devices/$device/resources
  echo clear > /sys/bus/pnp/devices/$device/resources
  echo set irq disabled > /sys/bus/pnp/devices/$device/resources
  echo fill > /sys/bus/pnp/devices/$device/resources
  echo activate > /sys/bus/pnp/devices/$device/resources

This patch addresses only the parsing of PnP ACPI devices.

ChangeLog (v1 -> v2):
 - extend patch description
 - fix typo in patch itself
Signed-off-by: Witold Szczeponik <Witold.Szczeponik@gmx.net>
Cc: Len Brown <lenb@kernel.org>
Cc: Adam Belay <abelay@mit.edu>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>