PCI/PM: Decode D3cold power state correctly

Use pci_power_name() to print pci_power_t correctly.  This changes:

  "state 0" or "D0"   to   "D0"
  "state 1" or "D1"   to   "D1"
  "state 2" or "D2"   to   "D2"
  "state 3" or "D3"   to   "D3hot"
  "state 4" or "D4"   to   "D3cold"

Changes dmesg logging only, no other functional change intended.

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Bjorn Helgaas <[email protected]>
Reviewed-by: Rafael J. Wysocki <[email protected]>
Reviewed-by: Keith Busch <[email protected]>
Reviewed-by: Mika Westerberg <[email protected]>

drivers/pci/pci.c

@@ -834,14 +834,16 @@ static int pci_raw_set_power_state(struct pci_dev *dev, pci_power_t state)
 		return -EINVAL;
 
 	/*
-	 * Validate current state:
-	 * Can enter D0 from any state, but if we can only go deeper
-	 * to sleep if we're already in a low power state
+	 * Validate transition: We can enter D0 from any state, but if
+	 * we're already in a low-power state, we can only go deeper.  E.g.,
+	 * we can go from D1 to D3, but we can't go directly from D3 to D1;
+	 * we'd have to go from D3 to D0, then to D1.
 	 */
 	if (state != PCI_D0 && dev->current_state <= PCI_D3cold
 	    && dev->current_state > state) {
-		pci_err(dev, "invalid power transition (from state %d to %d)\n",
-			dev->current_state, state);
+		pci_err(dev, "invalid power transition (from %s to %s)\n",
+			pci_power_name(dev->current_state),
+			pci_power_name(state));
 		return -EINVAL;
 	}
 
@@ -891,8 +893,9 @@ static int pci_raw_set_power_state(struct pci_dev *dev, pci_power_t state)
 	pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr);
 	dev->current_state = (pmcsr & PCI_PM_CTRL_STATE_MASK);
 	if (dev->current_state != state)
-		pci_info_ratelimited(dev, "Refused to change power state, currently in D%d\n",
-			 dev->current_state);
+		pci_info_ratelimited(dev, "refused to change power state from %s to %s\n",
+			 pci_power_name(dev->current_state),
+			 pci_power_name(state));
 
 	/*
 	 * According to section 5.4.1 of the "PCI BUS POWER MANAGEMENT