PCI: Avoid double hpmemsize MMIO window assignment

PCI: Avoid double hpmemsize MMIO window assignment

Previously, the kernel sometimes assigned more MMIO or MMIO_PREF space than
desired.  For example, if the user requested 128M of space with
"pci=realloc,hpmemsize=128M", we sometimes assigned 256M:

  pci 0000:06:01.0: BAR 14: assigned [mem 0x90100000-0xa00fffff] = 256M
  pci 0000:06:04.0: BAR 14: assigned [mem 0xa0200000-0xb01fffff] = 256M

With this patch applied:

  pci 0000:06:01.0: BAR 14: assigned [mem 0x90100000-0x980fffff] = 128M
  pci 0000:06:04.0: BAR 14: assigned [mem 0x98200000-0xa01fffff] = 128M

This happened when in the first pass, the MMIO_PREF succeeded but the MMIO
failed. In the next pass, because MMIO_PREF was already assigned, the
attempt to assign MMIO_PREF returned an error code instead of success
(nothing more to do, already allocated). Hence, the size which was actually
allocated, but thought to have failed, was placed in the MMIO window.

The bug resulted in the MMIO_PREF being added to the MMIO window, which
meant doubling if MMIO_PREF size = MMIO size. With a large MMIO_PREF, the
MMIO window would likely fail to be assigned altogether due to lack of
32-bit address space.

Change find_free_bus_resource() to do the following:

  - Return first unassigned resource of the correct type.
  - If there is none, return first assigned resource of the correct type.
  - If none of the above, return NULL.

Returning an assigned resource of the correct type allows the caller to
distinguish between already assigned and no resource of the correct type.

Add checks in pbus_size_io() and pbus_size_mem() to return success if
resource returned from find_free_bus_resource() is already allocated.

This avoids pbus_size_io() and pbus_size_mem() returning error code to
__pci_bus_size_bridges() when a resource has been successfully assigned in
a previous pass. This fixes the existing behaviour where space for a
resource could be reserved multiple times in different parent bridge
windows.

Link: https://lore.kernel.org/lkml/20190531171216.20532-2-logang@deltatee.com/T/#u
Link: https://bugzilla.kernel.org/show_bug.cgi?id=203243
Link: https://lore.kernel.org/r/PS2P216MB075563AA6AD242AA666EDC6A80760@PS2P216MB0755.KORP216.PROD.OUTLOOK.COM
Reported-by: Kit Chow <kchow@gigaio.com>
Reported-by: Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>