PCI/PM: Fix fallback to PCI_D0 in pci_platform_power_transition()

Commit b51306c (PCI: Set device power state to PCI_D0 for device
without native PM support) modified pci_platform_power_transition()
by adding code causing dev->current_state for devices that don't
support native PCI PM but are power-manageable by the platform to be
changed to PCI_D0 regardless of the value returned by the preceding
platform_pci_set_power_state().  In particular, that also is done
if the platform_pci_set_power_state() has been successful, which
causes the correct power state of the device set by
pci_update_current_state() in that case to be overwritten by PCI_D0.

Fix that mistake by making the fallback to PCI_D0 only happen if
the platform_pci_set_power_state() has returned an error.

[bhelgaas: folded in Yinghai's simplification, added URL & stable info]
Reference: http://lkml.kernel.org/r/27806FC4E5928A408B78E88BBC67A2306F466BBA@ORSMSX101.amr.corp.intel.com
Reported-by: Chris J. Benenati <chris.j.benenati@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>
Cc: <stable@vger.kernel.org>	# v3.2+

drivers/pci/pci.c

@@ -646,15 +646,11 @@ static int pci_platform_power_transition(struct pci_dev *dev, pci_power_t state)
 		error = platform_pci_set_power_state(dev, state);
 		if (!error)
 			pci_update_current_state(dev, state);
-		/* Fall back to PCI_D0 if native PM is not supported */
-		if (!dev->pm_cap)
-			dev->current_state = PCI_D0;
-	} else {
+	} else
 		error = -ENODEV;
-		/* Fall back to PCI_D0 if native PM is not supported */
-		if (!dev->pm_cap)
-			dev->current_state = PCI_D0;
-	}
+
+	if (error && !dev->pm_cap) /* Fall back to PCI_D0 */
+		dev->current_state = PCI_D0;
 
 	return error;
 }