PCI/PM: Add comments for PME poll support for PCIe

	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;