drivers: timer: nrf_grtc_timer: Add system_clock_disable implementation

drivers/timer/Kconfig.nrf_grtc

@@ -6,6 +6,7 @@ menuconfig NRF_GRTC_TIMER
 	default y
 	depends on DT_HAS_NORDIC_NRF_GRTC_ENABLED
 	select TICKLESS_CAPABLE
+	select SYSTEM_TIMER_HAS_DISABLE_SUPPORT
 	select TIMER_HAS_64BIT_CYCLE_COUNTER
 	select NRFX_GRTC
 	help

drivers/timer/nrf_grtc_timer.c

@@ -366,6 +366,10 @@ uint64_t z_nrf_grtc_timer_startup_value_get(void)
 #if defined(CONFIG_POWEROFF) && defined(CONFIG_NRF_GRTC_START_SYSCOUNTER)
 int z_nrf_grtc_wakeup_prepare(uint64_t wake_time_us)
 {
+	if (!nrfx_grtc_init_check()) {
+		return -ENOTSUP;
+	}
+
 	nrfx_err_t err_code;
 	static uint8_t systemoff_channel;
 	uint64_t now = counter();
@@ -463,6 +467,21 @@ ISR_DIRECT_DECLARE(nrfx_grtc_direct_irq_handler)
 }
 #endif
 
+void sys_clock_disable(void)
+{
+	nrfx_grtc_uninit();
+#if defined(CONFIG_CLOCK_CONTROL_NRF)
+	int err;
+	struct onoff_manager *mgr =
+		z_nrf_clock_control_get_onoff((clock_control_subsys_t)CLOCK_CONTROL_NRF_TYPE_LFCLK);
+
+	err = onoff_release(mgr);
+	__ASSERT_NO_MSG(err >= 0);
+
+	nrfx_coredep_delay_us(1000);
+#endif
+}
+
 static int sys_clock_driver_init(void)
 {
 	nrfx_err_t err_code;

samples/boards/nordic/system_off/Kconfig

@@ -23,4 +23,9 @@ config LPCOMP_WAKEUP_ENABLE
 	help
 	  Enable system off wakeup from analog comparator.
 
+config SYS_CLOCK_DISABLE
+	bool "Power down system clock before system off"
+	help
+	  System clock and GRTC will be switched off during system off.
+
 source "Kconfig.zephyr"

samples/boards/nordic/system_off/sample.yaml

@@ -47,6 +47,44 @@ tests:
         - "Off count: 0"
         - "Active Ticks:"
         - "Entering system off; press sw0 to restart"
+  sample.boards.nrf.system_off.grtc_off:
+    platform_allow:
+      - nrf54l15dk/nrf54l05/cpuapp
+      - nrf54l15dk/nrf54l10/cpuapp
+      - nrf54l15dk/nrf54l15/cpuapp
+      - nrf54lm20dk/nrf54lm20a/cpuapp
+    extra_configs:
+      - CONFIG_SYS_CLOCK_DISABLE=y
+    harness: console
+    harness_config:
+      type: multi_line
+      ordered: true
+      regex:
+        - "system off demo"
+        - "Retained data not supported"
+        - "System clock will be disabled"
+        - "Entering system off; press sw0 to restart"
+  sample.boards.nrf.system_off.retained_mem.grtc_off:
+    platform_allow:
+      - nrf54l15dk/nrf54l05/cpuapp
+      - nrf54l15dk/nrf54l10/cpuapp
+      - nrf54l15dk/nrf54l15/cpuapp
+      - nrf54lm20dk/nrf54lm20a/cpuapp
+    extra_configs:
+      - CONFIG_APP_USE_RETAINED_MEM=y
+      - CONFIG_SYS_CLOCK_DISABLE=y
+    harness: console
+    harness_config:
+      type: multi_line
+      ordered: true
+      regex:
+        - "system off demo"
+        - "Retained data: valid"
+        - "Boot count: 1"
+        - "Off count: 0"
+        - "Active Ticks:"
+        - "System clock will be disabled"
+        - "Entering system off; press sw0 to restart"
   sample.boards.nrf.system_off.grtc_wakeup:
     platform_allow:
       - nrf54l15dk/nrf54l05/cpuapp

samples/boards/nordic/system_off/src/main.c

@@ -17,6 +17,7 @@
 #include <zephyr/pm/device.h>
 #include <zephyr/sys/poweroff.h>
 #include <zephyr/sys/util.h>
+#include <zephyr/drivers/timer/system_timer.h>
 
 #define NON_WAKEUP_RESET_REASON (RESET_PIN | RESET_SOFTWARE | RESET_POR | RESET_DEBUG)
 
@@ -97,11 +98,15 @@ int main(void)
 		printf("Retained data not supported\n");
 	}
 
+#if defined(CONFIG_SYS_CLOCK_DISABLE)
+	printf("System clock will be disabled\n");
+#endif
 #if defined(CONFIG_GRTC_WAKEUP_ENABLE)
 	int err = z_nrf_grtc_wakeup_prepare(DEEP_SLEEP_TIME_S * USEC_PER_SEC);
 
 	if (err < 0) {
 		printk("Unable to prepare GRTC as a wake up source (err = %d).\n", err);
+		return 0;
 	} else {
 		printk("Entering system off; wait %u seconds to restart\n", DEEP_SLEEP_TIME_S);
 	}
@@ -141,6 +146,9 @@ int main(void)
 	}
 
 	hwinfo_clear_reset_cause();
+#if defined(CONFIG_SYS_CLOCK_DISABLE)
+	sys_clock_disable();
+#endif
 	sys_poweroff();
 
 	return 0;