PCI/PM: Rearrange pci_set_power_state()

The part of pci_set_power_state() related to transitions into
low-power states is unnecessary convoluted, so clearly divide it
into the D3cold special case and the general case covering all of
the other states.

Also fix a potential issue with calling pci_bus_set_current_state()
to set the current state of all devices on the subordinate bus to
D3cold without checking if the power state of the parent bridge has
really changed to D3cold.

Link: https://lore.kernel.org/r/2139440.Mh6RI2rZIc@kreacher
Signed-off-by: Rafael J. Wysocki <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>
Reviewed-by: Mika Westerberg <[e-mail]>

drivers/pci/pci.c

···
 	if (state >= PCI_D3hot && (dev->dev_flags & PCI_DEV_FLAGS_NO_D3))
 		return 0;
 
-	/*
-	 * To put device in D3cold, we put device into D3hot in native
-	 * way, then put device into D3cold with platform ops
-	 */
-	error = pci_set_low_power_state(dev, state > PCI_D3hot ?
-					PCI_D3hot : state);
+	if (state == PCI_D3cold) {
+		/*
+		 * To put the device in D3cold, put it into D3hot in the native
+		 * way, then put it into D3cold using platform ops.
+		 */
+		error = pci_set_low_power_state(dev, PCI_D3hot);
 
-	if (pci_platform_power_transition(dev, state))
-		return error;
+		if (pci_platform_power_transition(dev, PCI_D3cold))
+			return error;
 
-	/* Powering off a bridge may power off the whole hierarchy */
-	if (state == PCI_D3cold)
-		pci_bus_set_current_state(dev->subordinate, PCI_D3cold);
+		/* Powering off a bridge may power off the whole hierarchy */
+		if (dev->current_state == PCI_D3cold)
+			pci_bus_set_current_state(dev->subordinate, PCI_D3cold);
+	} else {
+		error = pci_set_low_power_state(dev, state);
+
+		if (pci_platform_power_transition(dev, state))
+			return error;
+	}
 
 	return 0;
 }