feat(core/cpu): decouple CPU standby from CPU power down

Decoupled the CPU idle state (now called standby) from the CPU power down state.
This change allows future implementations requiring CPU standby — where the
core may be needed shortly after an event — to avoid transitioning to a deeper
power down state.

Signed-off-by: João Peixoto <[email protected]>

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

@@ -27,7 +27,15 @@ void cpu_arch_profile_init(cpuid_t cpuid, paddr_t load_addr)
     }
 }
 
-void cpu_arch_profile_idle()
+void cpu_arch_profile_standby()
+{
+    int32_t err = psci_standby();
+    if (err) {
+        ERROR("PSCI cpu%d standby failed with error %ld", cpu()->id, err);
+    }
+}
+
+void cpu_arch_profile_powerdown()
 {
     int64_t err = psci_power_down(PSCI_WAKEUP_IDLE);
     if (err) {

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

@@ -58,7 +58,7 @@ static void psci_wake_from_powerdown(void)
 
 static void psci_wake_from_idle(void)
 {
-    cpu_idle_wakeup();
+    cpu_standby_wakeup();
 }
 
 void psci_wake_from_off(void);

src/arch/armv8/armv8-r/cpu.c

@@ -12,7 +12,12 @@ void cpu_arch_profile_init(cpuid_t cpuid, paddr_t load_addr)
     UNUSED_ARG(load_addr);
 }
 
-void cpu_arch_profile_idle()
+void cpu_arch_profile_standby()
+{
+    __asm__ volatile("wfi");
+}
+
+void cpu_arch_profile_powerdown()
 {
     __asm__ volatile("wfi");
 }

src/arch/armv8/cpu.c

@@ -22,17 +22,32 @@ unsigned long cpu_id_to_mpidr(cpuid_t id)
     return platform_arch_cpuid_to_mpidr(&platform, id);
 }
 
-void cpu_arch_idle()
+void cpu_arch_standby()
 {
-    cpu_arch_profile_idle();
+    cpu_arch_profile_standby();
 
     /*
      * In case the profile implementation does not jump to a predefined wake-up point and just
-     * returns from the profile, manually rewind stack and jump to idle wake up. Therefore, we
+     * returns from the profile, manually rewind stack and jump to standby wake up. Therefore, we
      * should not return after this point.
      */
     __asm__ volatile("mov sp, %0\n\r"
-                     "b cpu_idle_wakeup\n\r" ::"r"(&cpu()->stack[STACK_SIZE]));
+                     "b cpu_standby_wakeup\n\r" ::"r"(&cpu()->stack[STACK_SIZE]));
 
-    ERROR("returned from idle wake up");
+    ERROR("returned from standby wake up");
+}
+
+void cpu_arch_powerdown()
+{
+    cpu_arch_profile_powerdown();
+
+    /*
+     * In case the profile implementation does not jump to a predefined wake-up point and just
+     * returns from the profile, manually rewind stack and jump to powerdown wake up. Therefore, we
+     * should not return after this point.
+     */
+    __asm__ volatile("mov sp, %0\n\r"
+                     "b cpu_powerdown_wakeup\n\r" ::"r"(&cpu()->stack[STACK_SIZE]));
+
+    ERROR("returned from powerdown wake up");
 }

src/arch/armv8/inc/arch/cpu.h

@@ -18,7 +18,8 @@ struct cpu_arch {
 
 unsigned long cpu_id_to_mpidr(cpuid_t id);
 void cpu_arch_profile_init(cpuid_t cpuid, paddr_t load_addr);
-void cpu_arch_profile_idle(void);
+void cpu_arch_profile_standby(void);
+void cpu_arch_profile_powerdown(void);
 
 extern cpuid_t CPU_MASTER;
 

src/arch/armv8/psci.c

@@ -86,7 +86,7 @@ static int32_t psci_cpu_off_handler(void)
     cpu()->vcpu->arch.psci_ctx.state = OFF;
     spin_unlock(&cpu()->vcpu->arch.psci_ctx.lock);
 
-    cpu_idle();
+    cpu_powerdown();
 
     spin_lock(&cpu()->vcpu->arch.psci_ctx.lock);
     cpu()->vcpu->arch.psci_ctx.state = ON;

src/arch/riscv/cpu.c

@@ -27,10 +27,18 @@ void cpu_arch_init(cpuid_t cpuid, paddr_t load_addr)
     }
 }
 
-void cpu_arch_idle(void)
+void cpu_arch_standby(void)
 {
     __asm__ volatile("wfi\n\t" ::: "memory");
     __asm__ volatile("mv sp, %0\n\r"
-                     "j cpu_idle_wakeup\n\r" ::"r"(&cpu()->stack[STACK_SIZE]));
-    ERROR("returned from idle wake up");
+                     "j cpu_standby_wakeup\n\r" ::"r"(&cpu()->stack[STACK_SIZE]));
+    ERROR("returned from standby wake up");
+}
+
+void cpu_arch_powerdown(void)
+{
+    __asm__ volatile("wfi\n\t" ::: "memory");
+    __asm__ volatile("mv sp, %0\n\r"
+                     "j cpu_powerdown_wakeup\n\r" ::"r"(&cpu()->stack[STACK_SIZE]));
+    ERROR("returned from powerdown wake up");
 }

src/core/cpu.c

@@ -89,18 +89,29 @@ void cpu_msg_handler(void)
     cpu()->handling_msgs = false;
 }
 
-void cpu_idle(void)
+void cpu_standby(void)
 {
-    cpu_arch_idle();
+    cpu_arch_standby();
 
     /**
-     * Should not return here. cpu should "wake up" from idle in cpu_idle_wakeup with a rewinded
-     * stack.
+     * Should not return here. cpu should "wake up" from standby in cpu_standby_wakeup with a
+     * rewinded stack.
      */
-    ERROR("Spurious idle wake up");
+    ERROR("Spurious standby wake up");
 }
 
-void cpu_idle_wakeup(void)
+void cpu_powerdown(void)
+{
+    cpu_arch_powerdown();
+
+    /**
+     * Should not return here. cpu should "wake up" from powerdown in cpu_powerdown_wakeup with a
+     * rewinded stack.
+     */
+    ERROR("Spurious powerdown wake up");
+}
+
+void cpu_standby_wakeup(void)
 {
     if (interrupts_check(interrupts_ipi_id)) {
         interrupts_clear(interrupts_ipi_id);
@@ -110,6 +121,15 @@ void cpu_idle_wakeup(void)
     if (cpu()->vcpu != NULL) {
         vcpu_run(cpu()->vcpu);
     } else {
-        cpu_idle();
+        cpu_standby();
+    }
+}
+
+void cpu_powerdown_wakeup(void)
+{
+    if (cpu()->vcpu != NULL) {
+        vcpu_run(cpu()->vcpu);
+    } else {
+        cpu_powerdown();
     }
 }

src/core/inc/cpu.h

@@ -67,11 +67,14 @@ void cpu_send_msg(cpuid_t cpu, struct cpu_msg* msg);
 bool cpu_get_msg(struct cpu_msg* msg);
 void cpu_msg_handler(void);
 void cpu_msg_set_handler(cpuid_t id, cpu_msg_handler_t handler);
-void cpu_idle(void);
-void cpu_idle_wakeup(void);
+void cpu_standby(void);
+void cpu_powerdown(void);
+void cpu_standby_wakeup(void);
+void cpu_powerdown_wakeup(void);
 
 void cpu_arch_init(cpuid_t cpu_id, paddr_t load_addr);
-void cpu_arch_idle(void);
+void cpu_arch_standby(void);
+void cpu_arch_powerdown(void);
 
 extern struct cpuif cpu_interfaces[];
 static inline struct cpuif* cpu_if(cpuid_t cpu_id)

src/core/vmm.c

@@ -140,6 +140,6 @@ void vmm_init()
         cpu_sync_barrier(&vm->sync);
         vcpu_run(cpu()->vcpu);
     } else {
-        cpu_idle();
+        cpu_powerdown();
     }
 }