PCI: Fix used_buses calculation in pci_scan_child_bus_extend()

pci_scan_bridge_extend() returns the subordinate bus number needed to cover
all the buses below a bridge.  pci_scan_child_bus_extend() computes the
number of buses to reserve by comparing that with the current max bus
number.  Previously it did the subtraction in the wrong order, so
'used_buses' was nonsense.

Subtract 'max' from 'cmax' as is done for the similar
pci_scan_bridge_extend() call in the following block.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=216000
Fixes: 3374c545c27c ("PCI: Account for all bridges on bus when distributing bus numbers")
Link: https://lore.kernel.org/r/20220905080232.36087-2-mika.westerberg@linux.intel.com
Reported-by: Chris Chiu <chris.chiu@canonical.com>
Tested-by: Chris Chiu <chris.chiu@canonical.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index c5286b0..4f940dc 100644 (file)
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2920,8 +2920,8 @@ static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
                 * hotplug bridges too much during the second scan below.
                 */
                used_buses++;
-               if (cmax - max > 1)
-                       used_buses += cmax - max - 1;
+               if (max - cmax > 1)
+                       used_buses += max - cmax - 1;
        }
 
        /* Scan bridges that need to be reconfigured */