[PATCH 2/2] PCI: Skip resource distribution when no hotplug bridges

[Bjorn Helgaas <helgaas@kernel.org>]

From: Bjorn Helgaas <bhelgaas@google.com>

If "hotplug_bridges == 0", "!dev->is_hotplug_bridge" is always true, so the
loop that divides the remaining resources among hotplug-capable bridges
does nothing.

Check for "hotplug_bridges == 0" earlier, so we don't even have to compute
the amount of remaining resources.  No functional change intended.

---

I'm pretty sure this patch preserves the previous behavior of
pci_bus_distribute_available_resources(), but I'm not sure that
behavior is what we want.

For example, in the following topology, when we process bus 10, we
find two non-hotplug bridges and no hotplug bridges, so IIUC we return
without distributing any resources to them.  But I would think we
should try to give 10:1c.0 more space if possible because it has a
hotplug bridge below it.

  00:1c.0: hotplug bridge to [bus 10-2f]
    10:1c.0: non-hotplug bridge to [bus 11-2e]
      11:00.0: hotplug bridge to [bus 12-2e]
    10:1c.1: non-hotplug bridge to [bus 2f]
---
 drivers/pci/setup-bus.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index af28af898e42..04adeebe8866 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -1887,6 +1887,9 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
 		return;
 	}
 
+	if (hotplug_bridges == 0)
+		return;
+
 	/*
 	 * Calculate the total amount of extra resource space we can
 	 * pass to bridges below this one.  This is basically the
@@ -1936,8 +1939,6 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
 		 * Distribute available extra resources equally between
 		 * hotplug-capable downstream ports taking alignment into
 		 * account.
-		 *
-		 * Here hotplug_bridges is always != 0.
 		 */
 		align = pci_resource_alignment(bridge, io_res);
 		io = div64_ul(available_io, hotplug_bridges);
-- 
2.22.0.410.gd8fdbe21b5-goog