LoongArch: Implement constant timer shutdown interface

When a cpu is hot-unplugged, it is put in idle state and the function
arch_cpu_idle_dead() is called. The timer interrupt for this processor
should be disabled, otherwise there will be pending timer interrupt for
the unplugged cpu, so that vcpu is prevented from giving up scheduling
when system is running in vm mode.

This patch implements the timer shutdown interface so that the constant
timer will be properly disabled when a CPU is hot-unplugged.
Reviewed-by: WANG Xuerui <git@xen0n.name>
Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/kernel/time.c

@@ -58,14 +58,16 @@ static int constant_set_state_oneshot(struct clock_event_device *evt)
 	return 0;
 }
 
-static int constant_set_state_oneshot_stopped(struct clock_event_device *evt)
+static int constant_set_state_periodic(struct clock_event_device *evt)
 {
+	unsigned long period;
 	unsigned long timer_config;
 
 	raw_spin_lock(&state_lock);
 
-	timer_config = csr_read64(LOONGARCH_CSR_TCFG);
-	timer_config &= ~CSR_TCFG_EN;
+	period = const_clock_freq / HZ;
+	timer_config = period & CSR_TCFG_VAL;
+	timer_config |= (CSR_TCFG_PERIOD | CSR_TCFG_EN);
 	csr_write64(timer_config, LOONGARCH_CSR_TCFG);
 
 	raw_spin_unlock(&state_lock);
@@ -73,16 +75,14 @@ static int constant_set_state_oneshot_stopped(struct clock_event_device *evt)
 	return 0;
 }
 
-static int constant_set_state_periodic(struct clock_event_device *evt)
+static int constant_set_state_shutdown(struct clock_event_device *evt)
 {
-	unsigned long period;
 	unsigned long timer_config;
 
 	raw_spin_lock(&state_lock);
 
-	period = const_clock_freq / HZ;
-	timer_config = period & CSR_TCFG_VAL;
-	timer_config |= (CSR_TCFG_PERIOD | CSR_TCFG_EN);
+	timer_config = csr_read64(LOONGARCH_CSR_TCFG);
+	timer_config &= ~CSR_TCFG_EN;
 	csr_write64(timer_config, LOONGARCH_CSR_TCFG);
 
 	raw_spin_unlock(&state_lock);
@@ -90,11 +90,6 @@ static int constant_set_state_periodic(struct clock_event_device *evt)
 	return 0;
 }
 
-static int constant_set_state_shutdown(struct clock_event_device *evt)
-{
-	return 0;
-}
-
 static int constant_timer_next_event(unsigned long delta, struct clock_event_device *evt)
 {
 	unsigned long timer_config;
@@ -161,7 +156,7 @@ int constant_clockevent_init(void)
 	cd->rating = 320;
 	cd->cpumask = cpumask_of(cpu);
 	cd->set_state_oneshot = constant_set_state_oneshot;
-	cd->set_state_oneshot_stopped = constant_set_state_oneshot_stopped;
+	cd->set_state_oneshot_stopped = constant_set_state_shutdown;
 	cd->set_state_periodic = constant_set_state_periodic;
 	cd->set_state_shutdown = constant_set_state_shutdown;
 	cd->set_next_event = constant_timer_next_event;