linux-kernel - [PATCH 02/27] timecounter: Introduce timecounter_initialize to update timecounter and cyclecounter

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Date:   Fri, 15 Dec 2017 13:08:17 +0530
From:   Sagar Arun Kamble <sagar.a.kamble@...el.com>
To:     linux-kernel@...r.kernel.org
Cc:     Sagar Arun Kamble <sagar.a.kamble@...el.com>,
        Richard Cochran <richardcochran@...il.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...eaurora.org>
Subject: [PATCH 02/27] timecounter: Introduce timecounter_initialize to update timecounter and cyclecounter

With cyclecounter coupled with timecounter, we should move to use
interface that initializes entire timecounter structure. This patch
creates function timecounter_initialize that takes cyclecounter
parameters and start time and initializes the timecounter and underlying
cyclecounter.
Function timecounter_init which requires initialized cyclecounter can be
removed once all drivers are migrated to this new interface.

Suggested-by: Richard Cochran <richardcochran@...il.com>
Signed-off-by: Sagar Arun Kamble <sagar.a.kamble@...el.com>
Cc: Richard Cochran <richardcochran@...il.com>
Cc: Chris Wilson <chris@...is-wilson.co.uk>
Cc: John Stultz <john.stultz@...aro.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Stephen Boyd <sboyd@...eaurora.org>
Cc: linux-kernel@...r.kernel.org
---
 include/linux/timecounter.h | 41 ++++++++++++++++++++++++++++++++---------
 kernel/time/timecounter.c   | 18 ++++++++++++++++++
 2 files changed, 50 insertions(+), 9 deletions(-)

diff --git a/include/linux/timecounter.h b/include/linux/timecounter.h
index 6daca06..59d3fd7 100644
--- a/include/linux/timecounter.h
+++ b/include/linux/timecounter.h
@@ -46,13 +46,14 @@ struct cyclecounter {
 /**
  * struct timecounter - layer above a %struct cyclecounter which counts nanoseconds
  *	Contains the state needed by timecounter_read() to detect
- *	cycle counter wrap around. Initialize with
- *	timecounter_init(). Also used to convert cycle counts into the
- *	corresponding nanosecond counts with timecounter_cyc2time(). Users
- *	of this code are responsible for initializing the underlying
- *	cycle counter hardware, locking issues and reading the time
- *	more often than the cycle counter wraps around. The nanosecond
- *	counter will only wrap around after ~585 years.
+ *	cycle counter wrap around. Initialize with timecounter_init() when
+ *	underlying cyclecounter is initialized, with timecounter_initialize() to
+ *	initialize cyclecounter and timecounter fields. Also used to convert
+ *	cycle counts into the corresponding nanosecond counts with
+ *	timecounter_cyc2time(). Users of this code are responsible for
+ *	locking issues and reading the time more often than the cycle counter
+ *	wraps around. The nanosecond counter will only wrap around after ~585
+ *	years.
  *
  * @cc:			the cycle counter used by this instance
  * @cycle_last:		most recent cycle counter value seen by
@@ -108,8 +109,30 @@ extern void timecounter_init(struct timecounter *tc,
 			     u64 start_tstamp);
 
 /**
- * timecounter_read - return nanoseconds elapsed since timecounter_init()
- *                    plus the initial time stamp
+ * timecounter_initialize - initialize a time counter and underlying
+			    cyclecounter
+ * @tc:			Pointer to time counter which is to be initialized
+ * @read:		Pointer to function that returns the current cycle value
+ * @mask:		bitmask for two's complement
+ *			subtraction of non 64 bit counters,
+ * @mult:		cycle to nanosecond multiplier
+ * @shift:		cycle to nanosecond divisor (power of two)
+ * @start_tstamp:	Arbitrary initial time stamp.
+ *
+ * After this call the current cycle register (roughly) corresponds to
+ * the initial time stamp. Every call to timecounter_read() increments
+ * the time stamp counter by the number of elapsed nanoseconds.
+ */
+extern void timecounter_initialize(struct timecounter *tc,
+				   u64 (*read)(const struct cyclecounter *cc),
+				   u64 mask,
+				   u32 mult,
+				   u32 shift,
+				   u64 start_tstamp);
+
+/**
+ * timecounter_read - return nanoseconds elapsed since timecounter_init() or
+ *                    timecounter_initialize() plus the initial time stamp
  * @tc:          Pointer to time counter.
  *
  * In other words, keeps track of time since the same epoch as
diff --git a/kernel/time/timecounter.c b/kernel/time/timecounter.c
index 7919acb..6d915752 100644
--- a/kernel/time/timecounter.c
+++ b/kernel/time/timecounter.c
@@ -29,6 +29,24 @@ void timecounter_init(struct timecounter *tc, u64 start_tstamp)
 }
 EXPORT_SYMBOL_GPL(timecounter_init);
 
+void timecounter_initialize(struct timecounter *tc,
+			    u64 (*read)(const struct cyclecounter *cc),
+			    u64 mask,
+			    u32 mult,
+			    u32 shift,
+			    u64 start_tstamp)
+{
+	struct cyclecounter *cc = &tc->cc;
+
+	cc->read = read;
+	cc->mask = mask;
+	cc->mult = mult;
+	cc->shift = shift;
+
+	timecounter_init(tc, start_tstamp);
+}
+EXPORT_SYMBOL_GPL(timecounter_initialize);
+
 /**
  * timecounter_read_delta - get nanoseconds since last call of this function
  * @tc:         Pointer to time counter
-- 
1.9.1