PCI: Workaround missing pci_set_master in pci drivers

Ben Herrenschmidt found that commit 928bea964827 ("PCI: Delay enabling
bridges until they're needed") breaks PCI in some powerpc environments.

The reason is that the PCIe port driver will call pci_enable_device() on
the bridge, so the device is enabled, but skips pci_set_master because
pcie_port_auto and no acpi on powerpc.

Because of that, pci_enable_bridge() later on (called as a result of the
child device driver doing pci_enable_device) will see the bridge as
already enabled and will not call pci_set_master() on it.

Fixed by add checking in pci_enable_bridge, and call pci_set_master
if driver skip that.

That will make the code more robot and wade off problem for missing
pci_set_master in drivers.

Reported-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/pci/pci.c

@@ -1155,8 +1155,14 @@ static void pci_enable_bridge(struct pci_dev *dev)
 
 	pci_enable_bridge(dev->bus->self);
 
-	if (pci_is_enabled(dev))
+	if (pci_is_enabled(dev)) {
+		if (!dev->is_busmaster) {
+			dev_warn(&dev->dev, "driver skip pci_set_master, fix it!\n");
+			pci_set_master(dev);
+		}
 		return;
+	}
+
 	retval = pci_enable_device(dev);
 	if (retval)
 		dev_err(&dev->dev, "Error enabling bridge (%d), continuing\n",