[PATCH] arm/twd: avoid waking deeply sleeping CPUs for rate change notifier

[Lucas Stach]

The current clock notifier sends an IPI to all CPUs, even if they are in
deep sleep state with the local timer disabled and switched to tick
broadcast. This needlessly cuts the CPU sleep times, as nothing is gained
from updating a disabled TWDs rate.

Keep track of the enabled TWDs and only send an IPI to those CPUs with an
active local timer. As disabled TWDs may now miss a CPU frequency update
we need to make sure to refresh the rate on re-enabling of the timer.

Signed-off-by: Lucas Stach <l.stach at pengutronix.de>
---
 arch/arm/kernel/smp_twd.c | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/arch/arm/kernel/smp_twd.c b/arch/arm/kernel/smp_twd.c
index b30eafeef096..a3be30d30cc2 100644
--- a/arch/arm/kernel/smp_twd.c
+++ b/arch/arm/kernel/smp_twd.c
@@ -32,6 +32,8 @@ static struct clk *twd_clk;
 static unsigned long twd_timer_rate;
 static DEFINE_PER_CPU(bool, percpu_setup_called);
 
+static cpumask_var_t active_twd_mask;
+
 static struct clock_event_device __percpu *twd_evt;
 static unsigned int twd_features =
 		CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT;
@@ -39,12 +41,24 @@ static int twd_ppi;
 
 static int twd_shutdown(struct clock_event_device *clk)
 {
+	cpumask_clear_cpu(smp_processor_id(), active_twd_mask);
+
 	writel_relaxed(0, twd_base + TWD_TIMER_CONTROL);
 	return 0;
 }
 
 static int twd_set_oneshot(struct clock_event_device *clk)
 {
+	cpumask_set_cpu(smp_processor_id(), active_twd_mask);
+
+	/*
+	 * When going from shutdown to oneshot we might have missed some
+	 * frequency updates if the CPU was sleeping. Make sure to update
+	 * the timer frequency with the current rate.
+	 */
+	if (clockevent_state_shutdown(clk))
+		clockevents_update_freq(clk, twd_timer_rate);
+
 	/* period set, and timer enabled in 'next_event' hook */
 	writel_relaxed(TWD_TIMER_CONTROL_IT_ENABLE | TWD_TIMER_CONTROL_ONESHOT,
 		       twd_base + TWD_TIMER_CONTROL);
@@ -57,6 +71,16 @@ static int twd_set_periodic(struct clock_event_device *clk)
 			     TWD_TIMER_CONTROL_IT_ENABLE |
 			     TWD_TIMER_CONTROL_PERIODIC;
 
+	cpumask_set_cpu(smp_processor_id(), active_twd_mask);
+
+	/*
+	 * When going from shutdown to periodic we might have missed some
+	 * frequency updates if the CPU was sleeping. Make sure to update
+	 * the timer frequency with the current rate.
+	 */
+	if (clockevent_state_shutdown(clk))
+		clockevents_update_freq(clk, twd_timer_rate);
+
 	writel_relaxed(DIV_ROUND_CLOSEST(twd_timer_rate, HZ),
 		       twd_base + TWD_TIMER_LOAD);
 	writel_relaxed(ctrl, twd_base + TWD_TIMER_CONTROL);
@@ -124,8 +148,8 @@ static int twd_rate_change(struct notifier_block *nb,
 	 * changing cpu.
 	 */
 	if (flags == POST_RATE_CHANGE)
-		on_each_cpu(twd_update_frequency,
-				  (void *)&cnd->new_rate, 1);
+		on_each_cpu_mask(active_twd_mask, twd_update_frequency,
+				 (void *)&cnd->new_rate, 1);
 
 	return NOTIFY_OK;
 }
@@ -326,6 +350,9 @@ static int __init twd_local_timer_common_register(struct device_node *np)
 {
 	int err;
 
+	if (!zalloc_cpumask_var(&active_twd_mask, GFP_KERNEL))
+		return -ENOMEM;
+
 	twd_evt = alloc_percpu(struct clock_event_device);
 	if (!twd_evt) {
 		err = -ENOMEM;
-- 
2.16.3