[PATCH v2 3/3] drivers: clocksource: add CPU PM notifier for ARM architected timer

[Sudeep KarkadaNagesha]

From: Sudeep KarkadaNagesha <sudeep.karkadanagesha at arm.com>

Few control settings done in architected timer as part of initialisation
can be lost when CPU enters deeper power states. They need to be
re-initialised when the CPU is (warm)reset again.

This patch adds CPU PM notifiers to do the timer initialisation on warm
resets. It also save the event stream divider value calculated during
cold reset and uses the same in warm reset path.

Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
Reviewed-by: Will Deacon <will.deacon at arm.com>
Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha at arm.com>
---
 drivers/clocksource/arm_arch_timer.c | 38 +++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 6301ee5..7057552 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -13,6 +13,7 @@
 #include <linux/device.h>
 #include <linux/smp.h>
 #include <linux/cpu.h>
+#include <linux/cpu_pm.h>
 #include <linux/clockchips.h>
 #include <linux/interrupt.h>
 #include <linux/of_irq.h>
@@ -39,6 +40,8 @@ static struct clock_event_device __percpu *arch_timer_evt;
 
 static bool arch_timer_use_virtual = true;
 
+static int arch_timer_evtstream_div;
+
 /*
  * Architected system timer support.
  */
@@ -160,7 +163,9 @@ static int arch_timer_setup(struct clock_event_device *clk)
 	pos = fls(evt_stream_div);
 	if (pos > 1 && !(evt_stream_div & (1 << (pos - 2))))
 		pos--;
-	arch_counter_set_user_access(min(pos, 15));
+	/* save divider value for use in CPU PM notifier */
+	arch_timer_evtstream_div = min(pos, 15);
+	arch_counter_set_user_access(arch_timer_evtstream_div);
 
 	return 0;
 }
@@ -267,6 +272,31 @@ static struct notifier_block arch_timer_cpu_nb = {
 	.notifier_call = arch_timer_cpu_notify,
 };
 
+#ifdef CONFIG_CPU_PM
+static int arch_timer_cpu_pm_notify(struct notifier_block *self,
+				    unsigned long action, void *hcpu)
+{
+	if (action == CPU_PM_EXIT)
+		arch_counter_set_user_access(arch_timer_evtstream_div);
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block arch_timer_cpu_pm_notifier = {
+	.notifier_call = arch_timer_cpu_pm_notify,
+};
+
+static int __init arch_timer_cpu_pm_init(void)
+{
+	return cpu_pm_register_notifier(&arch_timer_cpu_pm_notifier);
+}
+#else
+static int __init arch_timer_cpu_pm_init(void)
+{
+	return 0;
+}
+#endif
+
 static int __init arch_timer_register(void)
 {
 	int err;
@@ -316,11 +346,17 @@ static int __init arch_timer_register(void)
 	if (err)
 		goto out_free_irq;
 
+	err = arch_timer_cpu_pm_init();
+	if (err)
+		goto out_unreg_notify;
+
 	/* Immediately configure the timer on the boot CPU */
 	arch_timer_setup(this_cpu_ptr(arch_timer_evt));
 
 	return 0;
 
+out_unreg_notify:
+	unregister_cpu_notifier(&arch_timer_cpu_nb);
 out_free_irq:
 	if (arch_timer_use_virtual)
 		free_percpu_irq(arch_timer_ppi[VIRT_PPI], arch_timer_evt);
-- 
1.8.1.2