[PATCH v6 1/3] PM: cpu: Add CPU_LAST_PM_ENTER and CPU_FIRST_PM_EXIT support

[Shawn Guo <shawn.guo@linaro.org>]

It becomes a common situation on some platforms that certain hardware
setup needs to be done on the last standing cpu, and rpmh-rsc[1] is such
an existing example.  As figuring out the last standing cpu is really
something generic, it adds CPU_LAST_PM_ENTER (and CPU_FIRST_PM_EXIT)
event support to cpu_pm helper, so that individual driver can be
notified when the last standing cpu is about to enter low power state.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/soc/qcom/rpmh-rsc.c?id=v5.16#n773

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
---
 include/linux/cpu_pm.h | 15 +++++++++++++++
 kernel/cpu_pm.c        | 33 +++++++++++++++++++++++++++++++--
 2 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/include/linux/cpu_pm.h b/include/linux/cpu_pm.h
index 552b8f9ea05e..153344307b7c 100644
--- a/include/linux/cpu_pm.h
+++ b/include/linux/cpu_pm.h
@@ -55,6 +55,21 @@ enum cpu_pm_event {
 
 	/* A cpu power domain is exiting a low power state */
 	CPU_CLUSTER_PM_EXIT,
+
+	/*
+	 * A cpu is entering a low power state after all other cpus
+	 * in the system have entered the lower power state.
+	 */
+	CPU_LAST_PM_ENTER,
+
+	/* The last cpu failed to enter a low power state */
+	CPU_LAST_PM_ENTER_FAILED,
+
+	/*
+	 * A cpu is exiting a low power state before any other cpus
+	 * in the system exits the low power state.
+	 */
+	CPU_FIRST_PM_EXIT,
 };
 
 #ifdef CONFIG_CPU_PM
diff --git a/kernel/cpu_pm.c b/kernel/cpu_pm.c
index 246efc74e3f3..7c104446e1e9 100644
--- a/kernel/cpu_pm.c
+++ b/kernel/cpu_pm.c
@@ -26,6 +26,8 @@ static struct {
 	.lock  = __RAW_SPIN_LOCK_UNLOCKED(cpu_pm_notifier.lock),
 };
 
+static atomic_t cpus_in_pm;
+
 static int cpu_pm_notify(enum cpu_pm_event event)
 {
 	int ret;
@@ -116,7 +118,20 @@ EXPORT_SYMBOL_GPL(cpu_pm_unregister_notifier);
  */
 int cpu_pm_enter(void)
 {
-	return cpu_pm_notify_robust(CPU_PM_ENTER, CPU_PM_ENTER_FAILED);
+	int ret;
+
+	ret = cpu_pm_notify_robust(CPU_PM_ENTER, CPU_PM_ENTER_FAILED);
+	if (ret)
+		return ret;
+
+	if (atomic_inc_return(&cpus_in_pm) == num_online_cpus()) {
+		ret = cpu_pm_notify_robust(CPU_LAST_PM_ENTER,
+					   CPU_LAST_PM_ENTER_FAILED);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(cpu_pm_enter);
 
@@ -134,7 +149,21 @@ EXPORT_SYMBOL_GPL(cpu_pm_enter);
  */
 int cpu_pm_exit(void)
 {
-	return cpu_pm_notify(CPU_PM_EXIT);
+	int ret;
+
+	ret = cpu_pm_notify(CPU_PM_EXIT);
+	if (ret)
+		return ret;
+
+	if (atomic_read(&cpus_in_pm) == num_online_cpus()) {
+		ret = cpu_pm_notify(CPU_FIRST_PM_EXIT);
+		if (ret)
+			return ret;
+	}
+
+	atomic_dec(&cpus_in_pm);
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(cpu_pm_exit);
 
-- 
2.25.1