feat(armv8/psci): Handle unexpected standby behavior

The development target zcu104 does not wake up on interrupts after emiting PSCI standby calls to TF-A. We should understand why. To circunvent this, we allow platforms to delcare standby is not supported and fallback to wfi

Signed-off-by: David Cerdeira <[email protected]>

src/arch/armv8/armv8-a/psci.c

@@ -82,6 +82,12 @@ void psci_wake(uint32_t handler_id)
 
 int32_t psci_standby()
 {
+    /* We've observed that some platforms behave unexpectedly when performing
+     * standby. In these cases, after standby, the CPU cores are not awaken
+     * by interrupts. */
+    if (!DEFINED(PLAT_PSCI_STANDBY_NOT_SUPPORTED)) {
+        return PSCI_E_NOT_SUPPORTED
+    }
     /* only apply request to core level */
     uint32_t pwr_state_aux = PSCI_POWER_STATE_LVL_0 | PSCI_STATE_TYPE_STANDBY;
 

src/arch/armv8/psci.c

@@ -69,14 +69,11 @@ static int32_t psci_cpu_suspend_handler(uint32_t power_state, unsigned long entr
         ret = psci_power_down(PSCI_WAKEUP_POWERDOWN);
     } else {
         // PSCI_STATE_TYPE_STANDBY:
-        /**
-         *  TODO: ideally we would emmit a standby request to PSCI (currently, ATF), but when we
-         * do, we do not wake up on interrupts on the current development target zcu104. We should
-         * understand why. To circunvent this, we directly emmit a wfi
-         */
-        // ret = psci_standby();
-        __asm__ volatile("wfi\n\r");
-        ret = PSCI_E_SUCCESS;
+        ret = psci_standby();
+        if(ret == PSCI_E_NOT_SUPPORTED){
+            __asm__ volatile("wfi\n\r");
+            ret = PSCI_E_SUCCESS;
+        }
     }
 
     return ret;

src/platform/zcu102/inc/plat/psci.h

@@ -13,4 +13,6 @@
 #define PSCI_STATE_TYPE_POWERDOWN (1UL << 30)
 #define PSCI_STATE_TYPE_BIT       (1UL << 30)
 
+#define PLAT_PSCI_STANDBY_NOT_SUPPORTED
+
 #endif // __PLAT_PSCI_H__