Bug 199581

Reported by Mika Westerberg <mika.westerberg@linux.intel.com> at https://lkml.kernel.org/r/20180416103453.46232-3-mika.westerberg@linux.intel.com :

When hot-adding a PCIe switch the way we currently distribute resources
does not always work well because devices connected to the switch might
need to have their MMIO resources aligned to something else than the
default 1 MB boundary. For example Intel Gigabit ET2 quad port server
adapter includes PCIe switch leading to 4 x GbE NIC devices that want
to have their MMIO resources aligned to 2 MB boundary instead.

The current resource distribution code does not take this alignment into
account and might try to add too much resources for the extension
hotplug bridge(s). The resulting bridge window is too big which makes
the resource assignment operation fail, and we are left with a bridge
window with minimal amount (1 MB) of MMIO space.

Here is what happens when an Intel Gigabit ET2 quad port server adapter
is hot-added:

  pci 0000:39:00.0: BAR 14: assigned [mem 0x53300000-0x6a0fffff]
                                          ^^^^^^^^^^
  pci 0000:3a:01.0: BAR 14: assigned [mem 0x53400000-0x547fffff]
                                          ^^^^^^^^^^
The above shows that the downstream bridge (3a:01.0) window is aligned
to 2 MB instead of 1 MB as is the upstream bridge (39:00.0) window. The
remaining MMIO space (0x15a00000) is assigned to the hotplug bridge
(3a:04.0) but it fails:

  pci 0000:3a:04.0: BAR 14: no space for [mem size 0x15a00000]
  pci 0000:3a:04.0: BAR 14: failed to assign [mem size 0x15a00000]