arch: Allow to specify memory for S2RAM resume

If the area, dedicated for the interrupt stack is not available, allow
to specify a memory region that will be used as the stack for the S2RAM
resume logic.

Signed-off-by: Tomasz Chyrowicz <[email protected]>

Author: tomchy

arch/arm/core/cortex_m/reset.S

@@ -101,6 +101,13 @@ SECTION_SUBSEC_FUNC(TEXT,_reset_section,__start)
 #endif /* CONFIG_INIT_ARCH_HW_AT_BOOT */
 
 #if defined(CONFIG_PM_S2RAM)
+#if DT_NODE_EXISTS(DT_NODELABEL(pm_s2ram_stack)) &&\
+	DT_NODE_HAS_COMPAT(DT_NODELABEL(pm_s2ram_stack), zephyr_memory_region)
+    /* If the assumption that the interrupt stack may be safely used is not met,
+     * use a predefined memory region to execute the S2RAM logic.
+     */
+    ldr r0, =DT_REG_ADDR(DT_NODELABEL(pm_s2ram_stack)) + DT_REG_SIZE(DT_NODELABEL(pm_s2ram_stack))
+#else
     /*
      * Temporarily set MSP to interrupt stack so that arch_pm_s2ram_resume can
      * use stack for calling pm_s2ram_mark_check_and_clear.
@@ -113,6 +120,7 @@ SECTION_SUBSEC_FUNC(TEXT,_reset_section,__start)
      * a short while, there is no change in behavior in either of the paths.
      */
     ldr r0, =z_interrupt_stacks + CONFIG_ISR_STACK_SIZE + MPU_GUARD_ALIGN_AND_SIZE
+#endif
     msr msp, r0
 
     bl arch_pm_s2ram_resume

boards/nordic/nrf54h20dk/nrf54h20dk_nrf54h20_cpuapp.dts

@@ -332,12 +332,19 @@ zephyr_udc0: &usbhs {
 
 /* Trim this RAM block for making room on all run-time common S2RAM cpu context. */
 &cpuapp_ram0 {
-	reg = <0x22000000 (DT_SIZE_K(32) - 32)>;
-	ranges = <0x0 0x22000000 (0x8000 - 0x20)>;
+	reg = <0x22000000 (DT_SIZE_K(32) - 48)>;
+	ranges = <0x0 0x22000000 (0x8000 - 0x30)>;
 };
 
 / {
 	soc {
+		/* temporary stack for S2RAM resume logic */
+		pm_s2ram_stack: cpuapp_s2ram_stack@22007fd0  {
+			compatible = "zephyr,memory-region", "mmio-sram";
+			reg = <0x22007fd0 16>;
+			zephyr,memory-region = "pm_s2ram_stack";
+		};
+
 		/* run-time common S2RAM cpu context RAM */
 		pm_s2ram: cpuapp_s2ram@22007fe0 {
 			compatible = "zephyr,memory-region", "mmio-sram";

subsys/pm/Kconfig

@@ -41,6 +41,11 @@ config PM_S2RAM
 	  When enabled on Cortex-M, and a 'zephyr,memory-region' compatible node with nodelabel
 	  'pm_s2ram' is defined in DT, _cpu_context symbol (located in arch/arm/core/cortex_m/pm_s2ram.c)
 	  is placed in linker section given by 'zephyr,memory-region' property of aforementioned node.
+	  Additionally on Cortex-M, if a 'zephyr,memory-region' compatible node with nodelabel
+	  'pm_s2ram_stack' is defined in DT, this region will be used as a temporary program stack
+	  for the S2RAM resume logic. The assembly reset handling code itself makes a single push of
+	  the return address, but the SoC-specific function (pm_s2ram_mark_check_and_clear) must be
+	  analyzed to determine the required stack size.
 
 config PM_S2RAM_CUSTOM_MARKING
 	bool "Use custom marking functions"