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Subject[PATCH 2/3] cpuidle: Add some comments in the cpuidle_enter function
Date
The code is a bit poor in comments. Fix that by adding some comments in the
cpuidle enter function.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
---
drivers/cpuidle/cpuidle.c | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 1220dac..5e6c6be 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -162,19 +162,50 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,

trace_cpu_idle_rcuidle(index, dev->cpu);

+ /*
+ * Store the idle start time for this cpu, this information
+ * will be used by cpuidle to measure how long the cpu has
+ * been idle and by the scheduler to prevent to wake it up too
+ * early
+ */
target_state->idle_stamp = ktime_to_us(ktime_get());

+ /*
+ * The enter to the low level idle routine. This call will block
+ * until an interrupt occurs meaning it is the end of the idle
+ * period
+ */
entered_state = target_state->enter(dev, drv, index);

+ /*
+ * Measure as soon as possible the duration of the idle
+ * period. It MUST be done before re-enabling the interrupt in
+ * order to prevent to add in the idle time measurement the
+ * interrupt handling duration
+ */
diff = ktime_to_us(ktime_sub_us(ktime_get(), target_state->idle_stamp));

+ /*
+ * Reset the idle time stamp as the scheduler may think the cpu is idle
+ * while it is in the process of waking up
+ */
target_state->idle_stamp = 0;

trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);

+ /*
+ * The cpuidle_enter_coupled uses the cpuidle_enter function.
+ * Don't re-enable the interrupts and let the enter_coupled
+ * function to wait for all cpus to sync and to enable the
+ * interrupts again from there
+ */
if (!cpuidle_state_is_coupled(dev, drv, entered_state))
local_irq_enable();

+ /*
+ * The idle duration will be casted to an integer, prevent to
+ * overflow by setting a boundary to INT_MAX
+ */
if (diff > INT_MAX)
diff = INT_MAX;

--
1.9.1


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