4.17-stable review patch. If anyone has any objections, please let me know.
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From: Mika Westerberg mika.westerberg@linux.intel.com
commit 3374c545c27c5350b954d1ab03c880d5502e5eba upstream.
When distributing extra bus number space to hotplug bridges for future extension, we don't account for the fact that there might be non-hotplug bridges on the bus after the hotplug bridges. For example:
01:00.0 --+- 02:00.0 (HotPlug-) -- Thunderbolt host controller +- 02:01.0 (HotPlug+) - 02:02.0 (HotPlug-) -- xHCI host controller
pci_scan_child_bus_extend() is supposed to distribute the remaining bus numbers to the hotplug bridge at 02:01.0, but only after accounting for all bridges on bus 02. Since we don't check whether there's another non-hotplug bridge after the hotplug bridge 02:01.0, it may not leave space for the non-hotplug bridge:
pci 0000:00:1b.0: PCI bridge to [bus 01-39] (Root Port) pci 0000:01:00.0: PCI bridge to [bus 02-39] ... pci 0000:02:00.0: PCI bridge to [bus 03] pci 0000:02:01.0: PCI bridge to [bus 04] pci_bus 0000:04: [bus 04-39] extended by 0x35 pci_bus 0000:04: bus scan returning with max=39 pci_bus 0000:04: busn_res: [bus 04-39] end is updated to 39 pci 0000:02:02.0: scanning [bus 00-00] behind bridge, pass 1 pci_bus 0000:3a: scanning bus pci_bus 0000:3a: bus scan returning with max=3a pci_bus 0000:3a: busn_res: [bus 3a] end is updated to 3a pci_bus 0000:3a: [bus 3a] partially hidden behind bridge 0000:02 [bus 02-39] pci_bus 0000:3a: [bus 3a] partially hidden behind bridge 0000:01 [bus 01-39] pci_bus 0000:02: bus scan returning with max=3a pci_bus 0000:02: busn_res: [bus 02-39] end can not be updated to 3a
The resulting 'lspci -t' output looks like this:
+-1b.0-[01-39]----00.0-[02-3a]--+-00.0-[03]----00.0 ^^ +-01.0-[04-39]-- -02.0-[3a]----00.0 ^^ The xHCI host controller behind 02:02.0 is not usable because it would have to be assigned bus 3a, which is not accessible through 00:1b.0.
To fix this, reserve at least one bus for each bridge while scanning already configured bridges. Then use this information in the second scan to correct the available extra bus space for hotplug bridges.
After this change the 'lspci -t' output is what is expected:
+-1b.0-[01-39]----00.0-[02-39]--+-00.0-[03]----00.0 +-01.0-[04-38]-- -02.0-[39]----00.0
The xHCI controller is now on bus 39, where it is usable.
Fixes: 1c02ea810065 ("PCI: Distribute available buses to hotplug-capable bridges") Reported-by: Mario Limonciello mario.limonciello@dell.com Signed-off-by: Mika Westerberg mika.westerberg@linux.intel.com [bhelgaas: changelog] Signed-off-by: Bjorn Helgaas bhelgaas@google.com Reviewed-by: Rafael J. Wysocki rafael.j.wysocki@intel.com Reviewed-by: Andy Shevchenko andriy.shevchenko@linux.intel.com Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/pci/probe.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-)
--- a/drivers/pci/probe.c +++ b/drivers/pci/probe.c @@ -2638,7 +2638,14 @@ static unsigned int pci_scan_child_bus_e for_each_pci_bridge(dev, bus) { cmax = max; max = pci_scan_bridge_extend(bus, dev, max, 0, 0); - used_buses += cmax - max; + + /* + * Reserve one bus for each bridge now to avoid extending + * hotplug bridges too much during the second scan below. + */ + used_buses++; + if (cmax - max > 1) + used_buses += cmax - max - 1; }
/* Scan bridges that need to be reconfigured */ @@ -2661,12 +2668,14 @@ static unsigned int pci_scan_child_bus_e * bridges if any. */ buses = available_buses / hotplug_bridges; - buses = min(buses, available_buses - used_buses); + buses = min(buses, available_buses - used_buses + 1); }
cmax = max; max = pci_scan_bridge_extend(bus, dev, cmax, buses, 1); - used_buses += max - cmax; + /* One bus is already accounted so don't add it again */ + if (max - cmax > 1) + used_buses += max - cmax - 1; }
/*