PCI: Use downstream bridges for distributing resources

PCI: Use downstream bridges for distributing resources

7180c1d08639 ("PCI: Distribute available resources for root buses, too")
breaks BAR assignment on some devices:

  pci 0006:03:00.0: BAR 0 [mem 0x6300c0000000-0x6300c1ffffff 64bit pref]: assigned
  pci 0006:03:00.1: BAR 0 [mem 0x6300c2000000-0x6300c3ffffff 64bit pref]: assigned
  pci 0006:03:00.2: BAR 0 [mem size 0x00800000 64bit pref]: can't assign; no space
  pci 0006:03:00.0: VF BAR 0 [mem size 0x02000000 64bit pref]: can't assign; no space
  pci 0006:03:00.1: VF BAR 0 [mem size 0x02000000 64bit pref]: can't assign; no space

The apertures of domain 0006 before 7180c1d08639:

  6300c0000000-63ffffffffff : PCI Bus 0006:00
    6300c0000000-6300c9ffffff : PCI Bus 0006:01
      6300c0000000-6300c9ffffff : PCI Bus 0006:02        # 160MB
        6300c0000000-6300c8ffffff : PCI Bus 0006:03      #   144MB
          6300c0000000-6300c1ffffff : 0006:03:00.0       #     32MB
          6300c2000000-6300c3ffffff : 0006:03:00.1       #     32MB
          6300c4000000-6300c47fffff : 0006:03:00.2       #      8MB
          6300c4800000-6300c67fffff : 0006:03:00.0       #     32MB
          6300c6800000-6300c87fffff : 0006:03:00.1       #     32MB
        6300c9000000-6300c9bfffff : PCI Bus 0006:04      #    12MB
          6300c9000000-6300c9bfffff : PCI Bus 0006:05    #    12MB
            6300c9000000-6300c91fffff : PCI Bus 0006:06  #      2MB
            6300c9200000-6300c93fffff : PCI Bus 0006:07  #      2MB
            6300c9400000-6300c95fffff : PCI Bus 0006:08  #      2MB
            6300c9600000-6300c97fffff : PCI Bus 0006:09  #      2MB

After 7180c1d08639:

  6300c0000000-63ffffffffff : PCI Bus 0006:00
    6300c0000000-6300c9ffffff : PCI Bus 0006:01
      6300c0000000-6300c9ffffff : PCI Bus 0006:02        # 160MB
        6300c0000000-6300c43fffff : PCI Bus 0006:03      #    68MB
          6300c0000000-6300c1ffffff : 0006:03:00.0       #      32MB
          6300c2000000-6300c3ffffff : 0006:03:00.1       #      32MB
              --- no space ---      : 0006:03:00.2       #       8MB
              --- no space ---      : 0006:03:00.0       #      32MB
              --- no space ---      : 0006:03:00.1       #      32MB
        6300c4400000-6300c4dfffff : PCI Bus 0006:04      #    10MB
          6300c4400000-6300c4dfffff : PCI Bus 0006:05    #      10MB
            6300c4400000-6300c45fffff : PCI Bus 0006:06  #        2MB
            6300c4600000-6300c47fffff : PCI Bus 0006:07  #        2MB
            6300c4800000-6300c49fffff : PCI Bus 0006:08  #        2MB
            6300c4a00000-6300c4bfffff : PCI Bus 0006:09  #        2MB

We can see that the window to 0006:03 gets shrunken too much and 0006:04
eats away the window for 0006:03:00.2.

The offending commit distributes the upstream bridge's resources multiple
times to every downstream bridge, hence makes the aperture smaller than
desired because calculation of io_per_b, mmio_per_b and mmio_pref_per_b
becomes incorrect.

Instead, distribute downstream bridges' own resources to resolve the issue.

Link: https://lore.kernel.org/r/20241204022457.51322-1-kaihengf@nvidia.com
Fixes: 7180c1d08639 ("PCI: Distribute available resources for root buses, too")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=219540
Signed-off-by: Kai-Heng Feng <kaihengf@nvidia.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Chia-Lin Kao (AceLan) <acelan.kao@canonical.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Carol Soto <csoto@nvidia.com>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Chris Chiu <chris.chiu@canonical.com>