Revert "PCI: PM: Do not read power state in pci_enable_device_flags()"

Revert commit 4514d99 ("PCI: PM: Do not read power state in
pci_enable_device_flags()") that is reported to cause PCI device
initialization issues on some systems.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=213481
Link: https://lore.kernel.org/linux-acpi/YNDoGICcg0V8HhpQ@eldamar.lan
Reported-by: Michael <phyre@rogers.com>
Reported-by: Salvatore Bonaccorso <carnil@debian.org>
Fixes: 4514d99 ("PCI: PM: Do not read power state in pci_enable_device_flags()")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Author: rafaeljw

drivers/pci/pci.c

@@ -1900,11 +1900,21 @@ static int pci_enable_device_flags(struct pci_dev *dev, unsigned long flags)
 	int err;
 	int i, bars = 0;
 
-	if (atomic_inc_return(&dev->enable_cnt) > 1) {
-		pci_update_current_state(dev, dev->current_state);
-		return 0;		/* already enabled */
+	/*
+	 * Power state could be unknown at this point, either due to a fresh
+	 * boot or a device removal call.  So get the current power state
+	 * so that things like MSI message writing will behave as expected
+	 * (e.g. if the device really is in D0 at enable time).
+	 */
+	if (dev->pm_cap) {
+		u16 pmcsr;
+		pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr);
+		dev->current_state = (pmcsr & PCI_PM_CTRL_STATE_MASK);
 	}
 
+	if (atomic_inc_return(&dev->enable_cnt) > 1)
+		return 0;		/* already enabled */
+
 	bridge = pci_upstream_bridge(dev);
 	if (bridge)
 		pci_enable_bridge(bridge);