[PATCH] powercap/drivers/idle_inject: Specify idle state max latency

[Daniel Lezcano]

Currently the idle injection framework uses the play_idle() function
which puts the current CPU in an idle state. The idle state is the
deepest one, as specified by the latency constraint when calling the
subsequent play_idle_precise() function with the INT_MAX.

The idle_injection is used by the cpuidle_cooling device which
computes the idle / run duration to mitigate the temperature by
injecting idle cycles. The cooling device has no control on the depth
of the idle state.

Allow finer control of the idle injection mechanism by allowing to
specify the latency for the idle state. Thus the cooling device has
the ability to have a guarantee on the exit latency of the idle states
it is injecting.

Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
---
 drivers/powercap/idle_inject.c | 27 ++++++++++++++++++++++++++-
 include/linux/idle_inject.h    |  6 ++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/drivers/powercap/idle_inject.c b/drivers/powercap/idle_inject.c
index cd1270614cc6..15e6f9b8023f 100644
--- a/drivers/powercap/idle_inject.c
+++ b/drivers/powercap/idle_inject.c
@@ -61,12 +61,14 @@ struct idle_inject_thread {
  * @timer: idle injection period timer
  * @idle_duration_us: duration of CPU idle time to inject
  * @run_duration_us: duration of CPU run time to allow
+ * @latency_us: max allowed latency
  * @cpumask: mask of CPUs affected by idle injection
  */
 struct idle_inject_device {
 	struct hrtimer timer;
 	unsigned int idle_duration_us;
 	unsigned int run_duration_us;
+	unsigned int latency_us;
 	unsigned long int cpumask[0];
 };
 
@@ -138,7 +140,8 @@ static void idle_inject_fn(unsigned int cpu)
 	 */
 	iit->should_run = 0;
 
-	play_idle(READ_ONCE(ii_dev->idle_duration_us));
+	play_idle_precise(READ_ONCE(ii_dev->idle_duration_us) * NSEC_PER_USEC,
+			  READ_ONCE(ii_dev->latency_us) * NSEC_PER_USEC);
 }
 
 /**
@@ -169,6 +172,27 @@ void idle_inject_get_duration(struct idle_inject_device *ii_dev,
 	*idle_duration_us = READ_ONCE(ii_dev->idle_duration_us);
 }
 
+/**
+ * idle_inject_set_latency - set the maximum latency allowed
+ * @latency_us: set the latency requirement for the idle state
+ */
+void idle_inject_set_latency(struct idle_inject_device *ii_dev,
+			     unsigned int latency_us)
+{
+	WRITE_ONCE(ii_dev->latency_us, latency_us);
+}
+
+/**
+ * idle_inject_get_latency - get the allowed latency
+ *
+ * Return: an unsigned int corresponding to the latency requirement
+ * for the idle state
+ */
+unsigned int idle_inject_get_latency(struct idle_inject_device *ii_dev)
+{
+	return READ_ONCE(ii_dev->latency_us);
+}
+
 /**
  * idle_inject_start - start idle injections
  * @ii_dev: idle injection control device structure
@@ -297,6 +321,7 @@ struct idle_inject_device *idle_inject_register(struct cpumask *cpumask)
 	cpumask_copy(to_cpumask(ii_dev->cpumask), cpumask);
 	hrtimer_init(&ii_dev->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 	ii_dev->timer.function = idle_inject_timer_fn;
+	ii_dev->latency_us = UINT_MAX;
 
 	for_each_cpu(cpu, to_cpumask(ii_dev->cpumask)) {
 
diff --git a/include/linux/idle_inject.h b/include/linux/idle_inject.h
index a445cd1a36c5..b573fee589b9 100644
--- a/include/linux/idle_inject.h
+++ b/include/linux/idle_inject.h
@@ -26,4 +26,10 @@ void idle_inject_set_duration(struct idle_inject_device *ii_dev,
 void idle_inject_get_duration(struct idle_inject_device *ii_dev,
 				 unsigned int *run_duration_us,
 				 unsigned int *idle_duration_us);
+
+void idle_inject_set_latency(struct idle_inject_device *ii_dev,
+			     unsigned int latency_ns);
+
+unsigned int idle_inject_get_latency(struct idle_inject_device *ii_dev);
+
 #endif /* __IDLE_INJECT_H__ */
-- 
2.17.1