samples: boards: stm32: serial_wakeup: Minor changes

Cleanup sample yaml file and code comments.

Enable PM_DEVICE_RUNTIME mode.

Signed-off-by: Erwan Gouriou <erwan.gouriou@st.com>

samples/boards/stm32/power_mgmt/serial_wakeup/prj.conf

@@ -1,7 +1,8 @@
 CONFIG_PM=y
 CONFIG_PM_DEVICE=y
-CONFIG_PM_DEVICE_RUNTIME=n
+CONFIG_PM_DEVICE_RUNTIME=y
-CONFIG_PM_DEVICE_RUNTIME_EXCLUSIVE=n
+CONFIG_PM_DEVICE_RUNTIME_EXCLUSIVE=y
+
 CONFIG_SHELL=y
 
 CONFIG_DEBUG=n

samples/boards/stm32/power_mgmt/serial_wakeup/sample.yaml

@@ -4,8 +4,6 @@ tests:
   sample.boards.stm32.power_mgmt.serial_wakeup:
     tags:
       - UART
-      - Wake
-      - up
       - power
     harness: console
     harness_config:

samples/boards/stm32/power_mgmt/serial_wakeup/src/main.c

@@ -24,7 +24,8 @@ int main(void)
 #if CONFIG_PM_DEVICE
 	/* In PM_DEVICE modes, enable device as a wakeup source will prevent
 	 * system to switch it off (clock off, set pins to sleep configuration, ...)
-	 * It is not requested in PM mode only since this mode will not
+	 * It is not requested in CONFIG_PM mode only as in this case, device is not
+	 * suspended before stop mode entry.
 	 */
 
 	bool ret;