linux-kernel - [RFC v8 08/28] arch/s390/kernel/time: set ->min_delta_ticks and ->max_delta

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Message-Id: <20161119160055.12491-9-nicstange@gmail.com>
Date:   Sat, 19 Nov 2016 17:00:35 +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 08/28] arch/s390/kernel/time: set ->min_delta_ticks and ->max_delta_ticks

With the yet to come introduction of NTP correction awareness to the
clockevent core, drivers should report their valid ranges in units of
cycles to the latter.

Currently, the s390's CPU timer clockevent device is initialized as
follows:

  cd->min_delta_ns    = 1;
  cd->max_delta_ns    = LONG_MAX;

Note that the device's time to cycle conversion factor, i.e.
cd->mult / (2^cd->shift), is approx. equal to 4.

Hence, this would translate to

  cd->min_delta_ticks = 4;
  cd->max_delta_ticks = 4 * LONG_MAX;

However, a minimum value of 1ns is in the range of noise anyway and the
clockevent core will take care of this by increasing it to 1us or so.
Furthermore, 4*LONG_MAX will overflow the unsigned long argument the
clockevent devices gets programmed with.

Thus, initialize ->min_delta_ticks with 1 and ->max_delta_ticks with
ULONG_MAX.

Signed-off-by: Nicolai Stange <nicstange@...il.com>
---
 arch/s390/kernel/time.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index 33082f6..46f2073 100644
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -158,7 +158,9 @@ void init_cpu_timer(void)
 	cd->mult		= 16777;
 	cd->shift		= 12;
 	cd->min_delta_ns	= 1;
+	cd->min_delta_ticks	= 1;
 	cd->max_delta_ns	= LONG_MAX;
+	cd->max_delta_ticks	= ULONG_MAX;
 	cd->rating		= 400;
 	cd->cpumask		= cpumask_of(cpu);
 	cd->set_next_event	= s390_next_event;
-- 
2.10.2