linux-kernel - [RFC v8 11/28] clockevents: always initialize ->min_delta_ns and ->max_delta

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Message-Id: <20161119160055.12491-12-nicstange@gmail.com>
Date:   Sat, 19 Nov 2016 17:00:38 +0100
From:   Nicolai Stange <nicstange@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     John Stultz <john.stultz@...aro.org>, linux-kernel@...r.kernel.org,
        Nicolai Stange <nicstange@...il.com>
Subject: [RFC v8 11/28] clockevents: always initialize ->min_delta_ns and ->max_delta_ns

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@...il.com>
---
 kernel/time/clockevents.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index e73ac7f..4fcec08 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -442,6 +442,20 @@ 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) ||
+	    (dev->features & CLOCK_EVT_FEAT_DUMMY))
+		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 +472,8 @@ 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 +504,6 @@ 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 +529,7 @@ 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);
-- 
2.10.2