PCI/PM: Keep parent bridge active when probing device

This patch fixes the following bug:

http://marc.info/?l=linux-pci&m=134329923124234&w=2

The root cause of the bug is as follow.

If a device is not bound with the corresponding driver, the device
runtime PM will be disabled and the device will be put into suspended
state.  So that, the bridge/PCIe port connected to it may be put into
suspended and low power state.  When do probing for the device later,
because the bridge/PCIe port connected to it is in low power state,
the IO access to device may fail.

To solve the issue, the bridge/PCIe port connected to the device is
put into active state before probing.
Reported-by: NBjorn Mork <bjorn@mork.no>
Signed-off-by: NHuang Ying <ying.huang@intel.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Reviewed-by: NRafael J. Wysocki <rjw@sisk.pl>

drivers/pci/pci-driver.c

@@ -280,8 +280,12 @@ static long local_pci_probe(void *_ddi)
 {
 	struct drv_dev_and_id *ddi = _ddi;
 	struct device *dev = &ddi->dev->dev;
+	struct device *parent = dev->parent;
 	int rc;
 
+	/* The parent bridge must be in active state when probing */
+	if (parent)
+		pm_runtime_get_sync(parent);
 	/* Unbound PCI devices are always set to disabled and suspended.
 	 * During probe, the device is set to enabled and active and the
 	 * usage count is incremented.  If the driver supports runtime PM,
@@ -298,6 +302,8 @@ static long local_pci_probe(void *_ddi)
 		pm_runtime_set_suspended(dev);
 		pm_runtime_put_noidle(dev);
 	}
+	if (parent)
+		pm_runtime_put(parent);
 	return rc;
 }