PCI: reset pci device state to unknown state for resume

Considering below scenario:
1.Unload a PCI device's driver, the device ->current remains in PCI_D0.
2.Do suspend/resume circle. After that, BIOS puts the device to D3.
3.Reload the device driver. The calling pci_set_power_state in the
driver can't change the state to D0, as set_power_state thinks the
device is already in D0.

A bug is reported at http://bugzilla.kernel.org/show_bug.cgi?id=6024
Pat attached a patch at
http://marc.theaimsgroup.com/?l=linux-pci&m=114049761428561&w=2 for this
issue, but it's lost. As pci_set_power_state can handle D3 -> D0
correctly (restore config space), I simplified Patrick's patch.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Cc: Patrick Mochel <mochel@digitalimplant.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/pci/pci-driver.c

@@ -264,6 +264,13 @@ static int pci_device_remove(struct device * dev)
 		pci_dev->driver = NULL;
 	}
 
+	/*
+	 * If the device is still on, set the power state as "unknown",
+	 * since it might change by the next time we load the driver.
+	 */
+	if (pci_dev->current_state == PCI_D0)
+		pci_dev->current_state = PCI_UNKNOWN;
+
 	/*
 	 * We would love to complain here if pci_dev->is_enabled is set, that
 	 * the driver should have called pci_disable_device(), but the
@@ -288,6 +295,12 @@ static int pci_device_suspend(struct device * dev, pm_message_t state)
 		suspend_report_result(drv->suspend, i);
 	} else {
 		pci_save_state(pci_dev);
+		/*
+		 * mark its power state as "unknown", since we don't know if
+		 * e.g. the BIOS will change its device state when we suspend.
+		 */
+		if (pci_dev->current_state == PCI_D0)
+			pci_dev->current_state = PCI_UNKNOWN;
 	}
 	return i;
 }