dts: arm: st: c0: Add power states

Adds power-states node to support stop mode. As idle timer is used RTC.

Signed-off-by: Tomáš Juřena <[email protected]>

Author: jurenat

dts/arm/st/c0/stm32c0.dtsi

@@ -73,6 +73,7 @@
 / {
 	chosen {
 		zephyr,flash-controller = &flash;
+		zephyr,cortex-m-idle-timer = &rtc;
 	};
 
 	cpus {
@@ -83,6 +84,22 @@
 			device_type = "cpu";
 			compatible = "arm,cortex-m0+";
 			reg = <0>;
+			cpu-power-states = <&stop>;
+		};
+
+		power-states {
+			stop: stop {
+				compatible = "zephyr,power-state";
+				power-state-name = "suspend-to-idle";
+				/* It is really hard to establish these numbers precisely.
+				 * We are basing on RTC as a wakeup source with 62,5us tick.
+				 * It requires a proper margin. Additionally, sys_clock_announce
+				 * works within system tick boundaries (100us by default),
+				 * which also introduces some shift.
+				 */
+				min-residency-us = <400>;
+				exit-latency-us = <300>;
+			};
 		};
 	};