arch: arm: aarch32: Introduce z_arm_on_enter_cpu_idle_prepare() hook

Introduce an optional hook to be called when the CPU is made idle.
If needed, this hook can be used to prepare data for upcoming
call to z_arm_on_enter_cpu_idle(). The main difference is that
z_arm_on_enter_cpu_idle_prepare() hook is called before interrupts
are disabled.

Signed-off-by: Andrzej Kuroś <andrzej.kuros@nordicsemi.no>

arch/arm/Kconfig

@@ -53,6 +53,16 @@ config ARM_ON_ENTER_CPU_IDLE_HOOK
 	  If needed, this hook can be used to prevent the CPU from actually
 	  entering sleep by skipping the WFE/WFI instruction.
 
+config ARM_ON_ENTER_CPU_IDLE_PREPARE_HOOK
+	bool
+	help
+	  Enables a hook (z_arm_on_enter_cpu_idle_prepare()) that is called when
+	  the CPU is made idle (by k_cpu_idle() or k_cpu_atomic_idle()).
+	  If needed, this hook can prepare data to upcoming call to
+	  z_arm_on_enter_cpu_idle(). The z_arm_on_enter_cpu_idle_prepare differs
+	  from z_arm_on_enter_cpu_idle because it is called before interrupts are
+	  disabled.
+
 config ARM_ON_EXIT_CPU_IDLE
 	bool
 	help

arch/arm/core/cortex_m/cpu_idle.S

@@ -81,16 +81,24 @@ SECTION_FUNC(TEXT, z_arm_cpu_idle_init)
 	bx	lr
 
 SECTION_FUNC(TEXT, arch_cpu_idle)
-#ifdef CONFIG_TRACING
+#if defined(CONFIG_TRACING) || \
+    defined(CONFIG_ARM_ON_ENTER_CPU_IDLE_PREPARE_HOOK)
 	push	{r0, lr}
+
+#ifdef CONFIG_TRACING
 	bl	sys_trace_idle
+#endif
+#ifdef CONFIG_ARM_ON_ENTER_CPU_IDLE_PREPARE_HOOK
+	bl	z_arm_on_enter_cpu_idle_prepare
+#endif
+
 #if defined(CONFIG_ARMV6_M_ARMV8_M_BASELINE)
 	pop	{r0, r1}
 	mov	lr, r1
 #else
 	pop	{r0, lr}
 #endif /* CONFIG_ARMV6_M_ARMV8_M_BASELINE */
-#endif /* CONFIG_TRACING */
+#endif
 
 #if defined(CONFIG_ARMV7_M_ARMV8_M_MAINLINE)
 	/*
@@ -134,17 +142,24 @@ SECTION_FUNC(TEXT, arch_cpu_idle)
 	bx	lr
 
 SECTION_FUNC(TEXT, arch_cpu_atomic_idle)
-#ifdef CONFIG_TRACING
+#if defined(CONFIG_TRACING) || \
+    defined(CONFIG_ARM_ON_ENTER_CPU_IDLE_PREPARE_HOOK)
 	push	{r0, lr}
+
+#ifdef CONFIG_TRACING
 	bl	sys_trace_idle
+#endif
+#ifdef CONFIG_ARM_ON_ENTER_CPU_IDLE_PREPARE_HOOK
+	bl	z_arm_on_enter_cpu_idle_prepare
+#endif
+
 #if defined(CONFIG_ARMV6_M_ARMV8_M_BASELINE)
 	pop	{r0, r1}
 	mov	lr, r1
 #else
 	pop	{r0, lr}
 #endif /* CONFIG_ARMV6_M_ARMV8_M_BASELINE */
-#endif /* CONFIG_TRACING */
+#endif
-
 	/*
 	 * Lock PRIMASK while sleeping: wfe will still get interrupted by
 	 * incoming interrupts but the CPU will not service them right away.

include/zephyr/arch/arm/misc.h

@@ -51,6 +51,15 @@ extern bool z_arm_thread_is_in_user_mode(void);
 bool z_arm_on_enter_cpu_idle(void);
 #endif
 
+#if defined(CONFIG_ARM_ON_ENTER_CPU_IDLE_PREPARE_HOOK)
+/* Prototype of a hook that can be enabled to be called every time the CPU is
+ * made idle (the calls will be done from k_cpu_idle() and k_cpu_atomic_idle()).
+ * The function is called before interrupts are disabled and can prepare to
+ * upcoming call to z_arm_on_enter_cpu_idle.
+ */
+void z_arm_on_enter_cpu_idle_prepare(void);
+#endif
+
 #endif
 
 #ifdef __cplusplus