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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 10:05:51 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 10:05:51 +0000
commit5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch)
treea94efe259b9009378be6d90eb30d2b019d95c194 /kernel/time/jiffies.c
parentInitial commit. (diff)
downloadlinux-5d1646d90e1f2cceb9f0828f4b28318cd0ec7744.tar.xz
linux-5d1646d90e1f2cceb9f0828f4b28318cd0ec7744.zip
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'kernel/time/jiffies.c')
-rw-r--r--kernel/time/jiffies.c122
1 files changed, 122 insertions, 0 deletions
diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
new file mode 100644
index 000000000..65409abcc
--- /dev/null
+++ b/kernel/time/jiffies.c
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+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * This file contains the jiffies based clocksource.
+ *
+ * Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
+ */
+#include <linux/clocksource.h>
+#include <linux/jiffies.h>
+#include <linux/module.h>
+#include <linux/init.h>
+
+#include "timekeeping.h"
+
+
+/* Since jiffies uses a simple TICK_NSEC multiplier
+ * conversion, the .shift value could be zero. However
+ * this would make NTP adjustments impossible as they are
+ * in units of 1/2^.shift. Thus we use JIFFIES_SHIFT to
+ * shift both the nominator and denominator the same
+ * amount, and give ntp adjustments in units of 1/2^8
+ *
+ * The value 8 is somewhat carefully chosen, as anything
+ * larger can result in overflows. TICK_NSEC grows as HZ
+ * shrinks, so values greater than 8 overflow 32bits when
+ * HZ=100.
+ */
+#if HZ < 34
+#define JIFFIES_SHIFT 6
+#elif HZ < 67
+#define JIFFIES_SHIFT 7
+#else
+#define JIFFIES_SHIFT 8
+#endif
+
+static u64 jiffies_read(struct clocksource *cs)
+{
+ return (u64) jiffies;
+}
+
+/*
+ * The Jiffies based clocksource is the lowest common
+ * denominator clock source which should function on
+ * all systems. It has the same coarse resolution as
+ * the timer interrupt frequency HZ and it suffers
+ * inaccuracies caused by missed or lost timer
+ * interrupts and the inability for the timer
+ * interrupt hardware to accuratly tick at the
+ * requested HZ value. It is also not recommended
+ * for "tick-less" systems.
+ */
+static struct clocksource clocksource_jiffies = {
+ .name = "jiffies",
+ .rating = 1, /* lowest valid rating*/
+ .uncertainty_margin = 32 * NSEC_PER_MSEC,
+ .read = jiffies_read,
+ .mask = CLOCKSOURCE_MASK(32),
+ .mult = TICK_NSEC << JIFFIES_SHIFT, /* details above */
+ .shift = JIFFIES_SHIFT,
+ .max_cycles = 10,
+};
+
+__cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(jiffies_lock);
+__cacheline_aligned_in_smp seqcount_t jiffies_seq;
+
+#if (BITS_PER_LONG < 64)
+u64 get_jiffies_64(void)
+{
+ unsigned int seq;
+ u64 ret;
+
+ do {
+ seq = read_seqcount_begin(&jiffies_seq);
+ ret = jiffies_64;
+ } while (read_seqcount_retry(&jiffies_seq, seq));
+ return ret;
+}
+EXPORT_SYMBOL(get_jiffies_64);
+#endif
+
+EXPORT_SYMBOL(jiffies);
+
+static int __init init_jiffies_clocksource(void)
+{
+ return __clocksource_register(&clocksource_jiffies);
+}
+
+core_initcall(init_jiffies_clocksource);
+
+struct clocksource * __init __weak clocksource_default_clock(void)
+{
+ return &clocksource_jiffies;
+}
+
+static struct clocksource refined_jiffies;
+
+int register_refined_jiffies(long cycles_per_second)
+{
+ u64 nsec_per_tick, shift_hz;
+ long cycles_per_tick;
+
+
+
+ refined_jiffies = clocksource_jiffies;
+ refined_jiffies.name = "refined-jiffies";
+ refined_jiffies.rating++;
+
+ /* Calc cycles per tick */
+ cycles_per_tick = (cycles_per_second + HZ/2)/HZ;
+ /* shift_hz stores hz<<8 for extra accuracy */
+ shift_hz = (u64)cycles_per_second << 8;
+ shift_hz += cycles_per_tick/2;
+ do_div(shift_hz, cycles_per_tick);
+ /* Calculate nsec_per_tick using shift_hz */
+ nsec_per_tick = (u64)NSEC_PER_SEC << 8;
+ nsec_per_tick += (u32)shift_hz/2;
+ do_div(nsec_per_tick, (u32)shift_hz);
+
+ refined_jiffies.mult = ((u32)nsec_per_tick) << JIFFIES_SHIFT;
+
+ __clocksource_register(&refined_jiffies);
+ return 0;
+}