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    Subject[PATCH 3.16 308/357] Revert "PCI: Dont scan random busses in pci_scan_bridge()"
    Date
    3.16-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Bjorn Helgaas <bhelgaas@google.com>

    commit 7a0b33d4a45d30b9a838fba4efcd80b7b57d4d16 upstream.

    This reverts commit fc1b253141b3 ("PCI: Don't scan random busses in
    pci_scan_bridge()") because it breaks CardBus on some machines.

    David tested a Dell Latitude D505 that worked like this prior to
    fc1b253141b3:

    pci 0000:00:1e.0: PCI bridge to [bus 01]
    pci 0000:01:01.0: CardBus bridge to [bus 02-05]

    Note that the 01:01.0 CardBus bridge has a bus number aperture of
    [bus 02-05], but those buses are all outside the 00:1e.0 PCI bridge bus
    number aperture, so accesses to buses 02-05 never reach CardBus. This is
    later patched up by yenta_fixup_parent_bridge(), which changes the
    subordinate bus number of the 00:1e.0 PCI bridge:

    pci_bus 0000:01: Raising subordinate bus# of parent bus (#01) from #01 to #05

    With fc1b253141b3, pci_scan_bridge() fails immediately when it notices that
    we can't allocate a valid secondary bus number for the CardBus bridge, and
    CardBus doesn't work at all:

    pci 0000:01:01.0: can't allocate child bus 01 from [bus 01]

    I'd prefer to fix this by integrating the yenta_fixup_parent_bridge() logic
    into pci_scan_bridge() so we fix the bus number apertures up front. But
    I don't think we can do that before v3.17, so I'm going to revert this to
    avoid the problem while we're working on the long-term fix.

    Link: https://bugzilla.kernel.org/show_bug.cgi?id=83441
    Link: http://lkml.kernel.org/r/1409303414-5196-1-git-send-email-david.henningsson@canonical.com
    Reported-by: David Henningsson <david.henningsson@canonical.com>
    Tested-by: David Henningsson <david.henningsson@canonical.com>
    Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/pci/probe.c | 10 +++-------
    1 file changed, 3 insertions(+), 7 deletions(-)

    --- a/drivers/pci/probe.c
    +++ b/drivers/pci/probe.c
    @@ -838,16 +838,12 @@ int pci_scan_bridge(struct pci_bus *bus,
    goto out;
    }

    - if (max >= bus->busn_res.end) {
    - dev_warn(&dev->dev, "can't allocate child bus %02x from %pR\n",
    - max, &bus->busn_res);
    - goto out;
    - }
    -
    /* Clear errors */
    pci_write_config_word(dev, PCI_STATUS, 0xffff);

    - /* The bus will already exist if we are rescanning */
    + /* Prevent assigning a bus number that already exists.
    + * This can happen when a bridge is hot-plugged, so in
    + * this case we only re-scan this bus. */
    child = pci_find_bus(pci_domain_nr(bus), max+1);
    if (!child) {
    child = pci_add_new_bus(bus, dev, max+1);



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