1 files changed, 56 insertions, 51 deletions

diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index eeea1e950b72..a26036d37a38 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -1,5 +1,6 @@
 /*
- * sched_clock.c: support for extending counters to full 64-bit ns counter
+ * sched_clock.c: Generic sched_clock() support, to extend low level
+ *                hardware time counters to full 64-bit ns values.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
@@ -19,15 +20,15 @@
 #include <linux/bitops.h>
 
 /**
- * struct clock_read_data - data required to read from sched_clock
+ * struct clock_read_data - data required to read from sched_clock()
  *
- * @epoch_ns:           sched_clock value at last update
- * @epoch_cyc:          Clock cycle value at last update
+ * @epoch_ns:           sched_clock() value at last update
+ * @epoch_cyc:          Clock cycle value at last update.
  * @sched_clock_mask:   Bitmask for two's complement subtraction of non 64bit
- *                      clocks
- * @read_sched_clock:   Current clock source (or dummy source when suspended)
- * @mult:               Multipler for scaled math conversion
- * @shift:              Shift value for scaled math conversion
+ *                      clocks.
+ * @read_sched_clock:   Current clock source (or dummy source when suspended).
+ * @mult:               Multipler for scaled math conversion.
+ * @shift:              Shift value for scaled math conversion.
  *
  * Care must be taken when updating this structure; it is read by
  * some very hot code paths. It occupies <=40 bytes and, when combined
@@ -44,25 +45,26 @@ struct clock_read_data {
 };
 
 /**
- * struct clock_data - all data needed for sched_clock (including
+ * struct clock_data - all data needed for sched_clock() (including
  *                     registration of a new clock source)
  *
  * @seq:                Sequence counter for protecting updates. The lowest
  *                      bit is the index for @read_data.
  * @read_data:          Data required to read from sched_clock.
- * @wrap_kt:            Duration for which clock can run before wrapping
- * @rate:               Tick rate of the registered clock
- * @actual_read_sched_clock: Registered clock read function
+ * @wrap_kt:            Duration for which clock can run before wrapping.
+ * @rate:               Tick rate of the registered clock.
+ * @actual_read_sched_clock: Registered hardware level clock read function.
  *
  * The ordering of this structure has been chosen to optimize cache
- * performance. In particular seq and read_data[0] (combined) should fit
- * into a single 64 byte cache line.
+ * performance. In particular 'seq' and 'read_data[0]' (combined) should fit
+ * into a single 64-byte cache line.
  */
 struct clock_data {
-        seqcount_t seq;
-        struct clock_read_data read_data[2];
-        ktime_t wrap_kt;
-        unsigned long rate;
+        seqcount_t              seq;
+        struct clock_read_data  read_data[2];
+        ktime_t                 wrap_kt;
+        unsigned long           rate;
+
         u64 (*actual_read_sched_clock)(void);
 };
 
@@ -112,10 +114,10 @@ unsigned long long notrace sched_clock(void)
 /*
  * Updating the data required to read the clock.
  *
- * sched_clock will never observe mis-matched data even if called from
+ * sched_clock() will never observe mis-matched data even if called from
  * an NMI. We do this by maintaining an odd/even copy of the data and
- * steering sched_clock to one or the other using a sequence counter.
- * In order to preserve the data cache profile of sched_clock as much
+ * steering sched_clock() to one or the other using a sequence counter.
+ * In order to preserve the data cache profile of sched_clock() as much
  * as possible the system reverts back to the even copy when the update
  * completes; the odd copy is used *only* during an update.
  */
@@ -135,7 +137,7 @@ static void update_clock_read_data(struct clock_read_data *rd)
 }
 
 /*
- * Atomically update the sched_clock epoch.
+ * Atomically update the sched_clock() epoch.
  */
 static void update_sched_clock(void)
 {
@@ -146,9 +148,7 @@ static void update_sched_clock(void)
         rd = cd.read_data[0];
 
         cyc = cd.actual_read_sched_clock();
-        ns = rd.epoch_ns +
-             cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask,
-                       rd.mult, rd.shift);
+        ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask, rd.mult, rd.shift);
 
         rd.epoch_ns = ns;
         rd.epoch_cyc = cyc;
@@ -160,11 +160,12 @@ static enum hrtimer_restart sched_clock_poll(struct hrtimer *hrt)
 {
         update_sched_clock();
         hrtimer_forward_now(hrt, cd.wrap_kt);
+
         return HRTIMER_RESTART;
 }
 
-void __init sched_clock_register(u64 (*read)(void), int bits,
-                                 unsigned long rate)
+void __init
+sched_clock_register(u64 (*read)(void), int bits, unsigned long rate)
 {
         u64 res, wrap, new_mask, new_epoch, cyc, ns;
         u32 new_mult, new_shift;
@@ -177,51 +178,53 @@ void __init sched_clock_register(u64 (*read)(void), int bits,
 
         WARN_ON(!irqs_disabled());
 
-        /* calculate the mult/shift to convert counter ticks to ns. */
+        /* Calculate the mult/shift to convert counter ticks to ns. */
         clocks_calc_mult_shift(&new_mult, &new_shift, rate, NSEC_PER_SEC, 3600);
 
         new_mask = CLOCKSOURCE_MASK(bits);
         cd.rate = rate;
 
-        /* calculate how many nanosecs until we risk wrapping */
+        /* Calculate how many nanosecs until we risk wrapping */
         wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask, NULL);
         cd.wrap_kt = ns_to_ktime(wrap);
 
         rd = cd.read_data[0];
 
-        /* update epoch for new counter and update epoch_ns from old counter*/
+        /* Update epoch for new counter and update 'epoch_ns' from old counter*/
         new_epoch = read();
         cyc = cd.actual_read_sched_clock();
-        ns = rd.epoch_ns +
-             cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask,
-                       rd.mult, rd.shift);
+        ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask, rd.mult, rd.shift);
         cd.actual_read_sched_clock = read;
 
-        rd.read_sched_clock = read;
-        rd.sched_clock_mask = new_mask;
-        rd.mult = new_mult;
-        rd.shift = new_shift;
-        rd.epoch_cyc = new_epoch;
-        rd.epoch_ns = ns;
+        rd.read_sched_clock     = read;
+        rd.sched_clock_mask     = new_mask;
+        rd.mult                 = new_mult;
+        rd.shift                = new_shift;
+        rd.epoch_cyc            = new_epoch;
+        rd.epoch_ns             = ns;
+
         update_clock_read_data(&rd);
 
         r = rate;
         if (r >= 4000000) {
                 r /= 1000000;
                 r_unit = 'M';
-        } else if (r >= 1000) {
-                r /= 1000;
-                r_unit = 'k';
-        } else
-                r_unit = ' ';
-
-        /* calculate the ns resolution of this counter */
+        } else {
+                if (r >= 1000) {
+                        r /= 1000;
+                        r_unit = 'k';
+                } else {
+                        r_unit = ' ';
+                }
+        }
+
+        /* Calculate the ns resolution of this counter */
         res = cyc_to_ns(1ULL, new_mult, new_shift);
 
         pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lluns\n",
                 bits, r, r_unit, res, wrap);
 
-        /* Enable IRQ time accounting if we have a fast enough sched_clock */
+        /* Enable IRQ time accounting if we have a fast enough sched_clock() */
         if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
                 enable_sched_clock_irqtime();
 
@@ -231,7 +234,7 @@ void __init sched_clock_register(u64 (*read)(void), int bits,
 void __init sched_clock_postinit(void)
 {
         /*
-         * If no sched_clock function has been provided at that point,
+         * If no sched_clock() function has been provided at that point,
          * make it the final one one.
          */
         if (cd.actual_read_sched_clock == jiffy_sched_clock_read)
@@ -257,7 +260,7 @@ void __init sched_clock_postinit(void)
  * This function must only be called from the critical
  * section in sched_clock(). It relies on the read_seqcount_retry()
  * at the end of the critical section to be sure we observe the
- * correct copy of epoch_cyc.
+ * correct copy of 'epoch_cyc'.
  */
 static u64 notrace suspended_sched_clock_read(void)
 {
@@ -273,6 +276,7 @@ static int sched_clock_suspend(void)
         update_sched_clock();
         hrtimer_cancel(&sched_clock_timer);
         rd->read_sched_clock = suspended_sched_clock_read;
+
         return 0;
 }
 
@@ -286,13 +290,14 @@ static void sched_clock_resume(void)
 }
 
 static struct syscore_ops sched_clock_ops = {
-        .suspend = sched_clock_suspend,
-        .resume = sched_clock_resume,
+        .suspend        = sched_clock_suspend,
+        .resume         = sched_clock_resume,
 };
 
 static int __init sched_clock_syscore_init(void)
 {
         register_syscore_ops(&sched_clock_ops);
+
         return 0;
 }
 device_initcall(sched_clock_syscore_init);