diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 5485883..485cfa9 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1578,15 +1578,25 @@
 
 	pci_write_config_word(dev, dev->pm_cap + PCI_PM_CTRL, pmcsr);
 
-	/* PCI (as opposed to PCIe) PME requires that the device have
-	   its PME# line hooked up correctly. Not all hardware vendors
-	   do this, so the PME never gets delivered and the device
-	   remains asleep. The easiest way around this is to
-	   periodically walk the list of suspended devices and check
-	   whether any have their PME flag set. The assumption is that
-	   we'll wake up often enough anyway that this won't be a huge
-	   hit, and the power savings from the devices will still be a
-	   win. */
+	/*
+	 * PCI (as opposed to PCIe) PME requires that the device have
+	 * its PME# line hooked up correctly. Not all hardware vendors
+	 * do this, so the PME never gets delivered and the device
+	 * remains asleep. The easiest way around this is to
+	 * periodically walk the list of suspended devices and check
+	 * whether any have their PME flag set. The assumption is that
+	 * we'll wake up often enough anyway that this won't be a huge
+	 * hit, and the power savings from the devices will still be a
+	 * win.
+	 *
+	 * Although PCIe uses in-band PME message instead of PME# line
+	 * to report PME, PME does not work for some PCIe devices in
+	 * reality.  For example, there are devices that set their PME
+	 * status bits, but don't really bother to send a PME message;
+	 * there are PCI Express Root Ports that don't bother to
+	 * trigger interrupts when they receive PME messages from the
+	 * devices below.  So PME poll is used for PCIe devices too.
+	 */
 
 	if (dev->pme_poll) {
 		struct pci_pme_device *pme_dev;