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Date: Fri, 21 Aug 2015 11:52:05 -0700
From: "Christopher S. Hall" <christopher.s.hall@...el.com>
To: jeffrey.t.kirsher@...el.com, hpa@...or.com, mingo@...hat.com,
tglx@...utronix.de, john.stultz@...aro.org
Cc: richardcochran@...il.com, x86@...nel.org,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
intel-wired-lan@...ts.osuosl.org, peterz@...radead.org,
"Christopher S. Hall" <christopher.s.hall@...el.com>
Subject: [PATCH v3 1/4] Add correlated clocksource deriving system time from an auxiliary clocksource
Add struct correlated_cs with pointer to original clocksource and
function pointer to convert correlated clocksource to the original
Add get_correlated_timestamp() function which given specific correlated_cs
and correlated_ts convert correlated counter value to system time
Signed-off-by: Christopher S. Hall <christopher.s.hall@...el.com>
---
include/linux/clocksource.h | 33 +++++++++++++++++++++++
include/linux/timekeeping.h | 4 +++
kernel/time/timekeeping.c | 65 +++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 102 insertions(+)
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 278dd27..4bedadb 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -258,4 +258,37 @@ void acpi_generic_timer_init(void);
static inline void acpi_generic_timer_init(void) { }
#endif
+/*
+ * struct correlated_cs - Descriptor for a clocksource correlated to another
+ * clocksource
+ * @related_cs: Pointer to the related timekeeping clocksource
+ * @convert: Conversion function to convert a timestamp from
+ * the correlated clocksource to cycles of the related
+ * timekeeping clocksource
+ */
+struct correlated_cs {
+ struct clocksource *related_cs;
+ u64 (*convert)(struct correlated_cs *cs,
+ u64 cycles);
+};
+
+struct correlated_ts;
+
+/**
+ * struct correlated_ts - Descriptor for taking a correlated time stamp
+ * @get_ts: Function to read out a synced system and device
+ * timestamp
+ * @system_ts: The raw system clock timestamp
+ * @device_ts: The raw device timestamp
+ * @system_real: @system_ts converted to CLOCK_REALTIME
+ * @system_raw: @system_ts converted to CLOCK_MONOTONIC_RAW
+ */
+struct correlated_ts {
+ int (*get_ts)(struct correlated_ts *ts);
+ u64 system_ts;
+ u64 device_ts;
+ ktime_t system_real;
+ ktime_t system_raw;
+ void *private;
+};
#endif /* _LINUX_CLOCKSOURCE_H */
diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 6e191e4..a9e1a2d 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -258,6 +258,10 @@ extern void timekeeping_inject_sleeptime64(struct timespec64 *delta);
*/
extern void getnstime_raw_and_real(struct timespec *ts_raw,
struct timespec *ts_real);
+struct correlated_ts;
+struct correlated_cs;
+extern int get_correlated_timestamp(struct correlated_ts *crt,
+ struct correlated_cs *crs);
/*
* Persistent clock related interfaces
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index bca3667..90a7c6f 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -312,6 +312,19 @@ static inline s64 timekeeping_get_ns(struct tk_read_base *tkr)
return nsec + arch_gettimeoffset();
}
+static inline s64 timekeeping_convert_to_ns(struct tk_read_base *tkr,
+ cycle_t cycles)
+{
+ cycle_t delta;
+ s64 nsec;
+
+ /* calculate the delta since the last update_wall_time */
+ delta = clocksource_delta(cycles, tkr->cycle_last, tkr->mask);
+
+ nsec = delta * tkr->mult + tkr->xtime_nsec;
+ return nsec >> tkr->shift;
+}
+
/**
* update_fast_timekeeper - Update the fast and NMI safe monotonic timekeeper.
* @tkr: Timekeeping readout base from which we take the update
@@ -885,6 +898,58 @@ EXPORT_SYMBOL(getnstime_raw_and_real);
#endif /* CONFIG_NTP_PPS */
/**
+ * get_correlated_timestamp - Get a correlated timestamp
+ *
+ * Reads a timestamp from a device and correlates it to system time
+ */
+int get_correlated_timestamp(struct correlated_ts *crt,
+ struct correlated_cs *crs)
+{
+ struct timekeeper *tk = &tk_core.timekeeper;
+ unsigned long seq;
+ cycles_t cycles;
+ ktime_t base;
+ s64 nsecs;
+ int ret;
+
+ do {
+ seq = read_seqcount_begin(&tk_core.seq);
+ /*
+ * Verify that the correlated clocksoure is related to
+ * the currently installed timekeeper clocksoure
+ */
+ if (tk->tkr_mono.clock != crs->related_cs)
+ return -ENODEV;
+
+ /*
+ * Try to get a timestamp from the device.
+ */
+ ret = crt->get_ts(crt);
+ if (ret)
+ return ret;
+
+ /*
+ * Convert the timestamp to timekeeper clock cycles
+ */
+ cycles = crs->convert(crs, crt->system_ts);
+
+ /* Convert to clock realtime */
+ base = ktime_add(tk->tkr_mono.base,
+ tk_core.timekeeper.offs_real);
+ nsecs = timekeeping_convert_to_ns(&tk->tkr_mono, cycles);
+ crt->system_real = ktime_add_ns(base, nsecs);
+
+ /* Convert to clock raw monotonic */
+ base = tk->tkr_raw.base;
+ nsecs = timekeeping_convert_to_ns(&tk->tkr_raw, cycles);
+ crt->system_raw = ktime_add_ns(base, nsecs);
+
+ } while (read_seqcount_retry(&tk_core.seq, seq));
+ return 0;
+}
+EXPORT_SYMBOL(get_correlated_timestamp);
+
+/**
* do_gettimeofday - Returns the time of day in a timeval
* @tv: pointer to the timeval to be set
*
--
2.1.4
--
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