ACPI / PM: Add state information to error message in acpi_device_set_power()

The state information can be useful to know what the problem is when
an error message about a device can not being set to a higher power
state than its parent appeared, so this patch adds such state
information for both the target state of the device and the current
state of its parent.
Signed-off-by: NAaron Lu <aaron.lu@intel.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/device_pm.c

@@ -179,7 +179,9 @@ int acpi_device_set_power(struct acpi_device *device, int state)
 	}
 	if (device->parent && (state < device->parent->power.state)) {
 		dev_warn(&device->dev,
-			 "Cannot transition to a higher-powered state than parent\n");
+			 "Cannot transition to power state %s for parent in %s\n",
+			 acpi_power_state_string(state),
+			 acpi_power_state_string(device->parent->power.state));
 		return -ENODEV;
 	}