[RFC v6 11/23] clockevents: always initialize ->min_delta_ns and ->max_delta_ns

Nicolai Stange
2016-09-09T20:01:36Z

Now that all clockevent drivers set ->min_delta_ticks and ->max_delta_ticks
independently of whether they use clockevents_config*() or not, the
clockevent core can calculate ->min_delta_ns and ->max_delta_ns from these
unconditionally.

The goal is to prepare the clockevent core for introducing NTP rate
correction awareness: as the clockevent devices' rates will get adjusted,
the ->*_delta_ns won't stay fixed but need to get changed as well.

Thus, make the clockevent core calculate the ->*_delta_ns values from
the invariant ->_delta_ticks ones at device registration.

In order to facilitate this, move the corresponding code from
clockevents_config() into its own helper function,
__clockevents_update_bounds() and invoke this where needed, in
particular from clockevents_register_device().

Note that there is a side effect affecting those drivers
- not using clockevents_config*()
- and manually initializing their ->min_delta_ns to values less than 1us.
In order to avoid "pointless noise", the clockevent core always sets
->min_delta_ns to values >= 1us, and thus, those drivers' ->min_delta_ns
is now increased. I think that this side effect is desired though.

Signed-off-by: Nicolai Stange <nicstange@gmail.com>
---
kernel/time/clockevents.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index e73ac7f..f352f54 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -442,6 +442,19 @@ int clockevents_unbind_device(struct clock_event_device *ced, int cpu)
}
EXPORT_SYMBOL_GPL(clockevents_unbind_device);

+static void __clockevents_update_bounds(struct clock_event_device *dev)
+{
+ if (!(dev->features & CLOCK_EVT_FEAT_ONESHOT))
+ return;
+
+ /*
+ * cev_delta2ns() never returns values less than 1us and thus,
+ * we'll never program any ced with anything less.
+ */
+ dev->min_delta_ns = cev_delta2ns(dev->min_delta_ticks, dev, false);
+ dev->max_delta_ns = cev_delta2ns(dev->max_delta_ticks, dev, true);
+}
+
/**
* clockevents_register_device - register a clock event device
* @dev: device to register
@@ -458,6 +471,8 @@ void clockevents_register_device(struct clock_event_device *dev)
dev->cpumask = cpumask_of(smp_processor_id());
}

+ __clockevents_update_bounds(dev);
+
raw_spin_lock_irqsave(&clockevents_lock, flags);

list_add(&dev->list, &clockevent_devices);
@@ -488,8 +503,6 @@ static void clockevents_config(struct clock_event_device *dev, u32 freq)
sec = 600;

clockevents_calc_mult_shift(dev, freq, sec);
- dev->min_delta_ns = cev_delta2ns(dev->min_delta_ticks, dev, false);
- dev->max_delta_ns = cev_delta2ns(dev->max_delta_ticks, dev, true);
}

/**
@@ -515,6 +528,7 @@ EXPORT_SYMBOL_GPL(clockevents_config_and_register);
int __clockevents_update_freq(struct clock_event_device *dev, u32 freq)
{
clockevents_config(dev, freq);
+ __clockevents_update_bounds(dev);

if (clockevent_state_oneshot(dev))
return clockevents_program_event(dev, dev->next_event, false);
--
2.9.3