diff options
| -rw-r--r-- | include/linux/timekeeper_internal.h | 2 | ||||
| -rw-r--r-- | include/linux/timekeeping.h | 5 | ||||
| -rw-r--r-- | kernel/time/timekeeping.c | 171 |
3 files changed, 177 insertions, 1 deletions
diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h index 25247220b4b7..e88005459035 100644 --- a/include/linux/timekeeper_internal.h +++ b/include/linux/timekeeper_internal.h @@ -50,6 +50,7 @@ struct tk_read_base { * @offs_tai: Offset clock monotonic -> clock tai * @tai_offset: The current UTC to TAI offset in seconds * @clock_was_set_seq: The sequence number of clock was set events + * @cs_was_changed_seq: The sequence number of clocksource change events * @next_leap_ktime: CLOCK_MONOTONIC time value of a pending leap-second * @raw_time: Monotonic raw base time in timespec64 format * @cycle_interval: Number of clock cycles in one NTP interval @@ -91,6 +92,7 @@ struct timekeeper { ktime_t offs_tai; s32 tai_offset; unsigned int clock_was_set_seq; + u8 cs_was_changed_seq; ktime_t next_leap_ktime; struct timespec64 raw_time; diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h index 4a2ca65fc778..96f37bee3bc1 100644 --- a/include/linux/timekeeping.h +++ b/include/linux/timekeeping.h @@ -272,11 +272,15 @@ extern void ktime_get_raw_and_real_ts64(struct timespec64 *ts_raw, * @cycles: Clocksource counter value to produce the system times * @real: Realtime system time * @raw: Monotonic raw system time + * @clock_was_set_seq: The sequence number of clock was set events + * @cs_was_changed_seq: The sequence number of clocksource change events */ struct system_time_snapshot { cycle_t cycles; ktime_t real; ktime_t raw; + unsigned int clock_was_set_seq; + u8 cs_was_changed_seq; }; /* @@ -312,6 +316,7 @@ extern int get_device_system_crosststamp( struct system_counterval_t *system_counterval, void *ctx), void *ctx, + struct system_time_snapshot *history, struct system_device_crosststamp *xtstamp); /* diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index dba595cdb200..931b0b1a71e9 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -233,6 +233,7 @@ static void tk_setup_internals(struct timekeeper *tk, struct clocksource *clock) u64 tmp, ntpinterval; struct clocksource *old_clock; + ++tk->cs_was_changed_seq; old_clock = tk->tkr_mono.clock; tk->tkr_mono.clock = clock; tk->tkr_mono.read = clock->read; @@ -894,6 +895,8 @@ void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot) seq = read_seqcount_begin(&tk_core.seq); now = tk->tkr_mono.read(tk->tkr_mono.clock); + systime_snapshot->cs_was_changed_seq = tk->cs_was_changed_seq; + systime_snapshot->clock_was_set_seq = tk->clock_was_set_seq; base_real = ktime_add(tk->tkr_mono.base, tk_core.timekeeper.offs_real); base_raw = tk->tkr_raw.base; @@ -907,10 +910,123 @@ void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot) } EXPORT_SYMBOL_GPL(ktime_get_snapshot); +/* Scale base by mult/div checking for overflow */ +static int scale64_check_overflow(u64 mult, u64 div, u64 *base) +{ + u64 tmp, rem; + + tmp = div64_u64_rem(*base, div, &rem); + + if (((int)sizeof(u64)*8 - fls64(mult) < fls64(tmp)) || + ((int)sizeof(u64)*8 - fls64(mult) < fls64(rem))) + return -EOVERFLOW; + tmp *= mult; + rem *= mult; + + do_div(rem, div); + *base = tmp + rem; + return 0; +} + +/** + * adjust_historical_crosststamp - adjust crosstimestamp previous to current interval + * @history: Snapshot representing start of history + * @partial_history_cycles: Cycle offset into history (fractional part) + * @total_history_cycles: Total history length in cycles + * @discontinuity: True indicates clock was set on history period + * @ts: Cross timestamp that should be adjusted using + * partial/total ratio + * + * Helper function used by get_device_system_crosststamp() to correct the + * crosstimestamp corresponding to the start of the current interval to the + * system counter value (timestamp point) provided by the driver. The + * total_history_* quantities are the total history starting at the provided + * reference point and ending at the start of the current interval. The cycle + * count between the driver timestamp point and the start of the current + * interval is partial_history_cycles. + */ +static int adjust_historical_crosststamp(struct system_time_snapshot *history, + cycle_t partial_history_cycles, + cycle_t total_history_cycles, + bool discontinuity, + struct system_device_crosststamp *ts) +{ + struct timekeeper *tk = &tk_core.timekeeper; + u64 corr_raw, corr_real; + bool interp_forward; + int ret; + + if (total_history_cycles == 0 || partial_history_cycles == 0) + return 0; + + /* Interpolate shortest distance from beginning or end of history */ + interp_forward = partial_history_cycles > total_history_cycles/2 ? + true : false; + partial_history_cycles = interp_forward ? + total_history_cycles - partial_history_cycles : + partial_history_cycles; + + /* + * Scale the monotonic raw time delta by: + * partial_history_cycles / total_history_cycles + */ + corr_raw = (u64)ktime_to_ns( + ktime_sub(ts->sys_monoraw, history->raw)); + ret = scale64_check_overflow(partial_history_cycles, + total_history_cycles, &corr_raw); + if (ret) + return ret; + + /* + * If there is a discontinuity in the history, scale monotonic raw + * correction by: + * mult(real)/mult(raw) yielding the realtime correction + * Otherwise, calculate the realtime correction similar to monotonic + * raw calculation + */ + if (discontinuity) { + corr_real = mul_u64_u32_div + (corr_raw, tk->tkr_mono.mult, tk->tkr_raw.mult); + } else { + corr_real = (u64)ktime_to_ns( + ktime_sub(ts->sys_realtime, history->real)); + ret = scale64_check_overflow(partial_history_cycles, + total_history_cycles, &corr_real); + if (ret) + return ret; + } + + /* Fixup monotonic raw and real time time values */ + if (interp_forward) { + ts->sys_monoraw = ktime_add_ns(history->raw, corr_raw); + ts->sys_realtime = ktime_add_ns(history->real, corr_real); + } else { + ts->sys_monoraw = ktime_sub_ns(ts->sys_monoraw, corr_raw); + ts->sys_realtime = ktime_sub_ns(ts->sys_realtime, corr_real); + } + + return 0; +} + +/* + * cycle_between - true if test occurs chronologically between before and after + */ +static bool cycle_between(cycle_t before, cycle_t test, cycle_t after) +{ + if (test > before && test < after) + return true; + if (test < before && before > after) + return true; + return false; +} + /** * get_device_system_crosststamp - Synchronously capture system/device timestamp - * @sync_devicetime: Callback to get simultaneous device time and + * @get_time_fn: Callback to get simultaneous device time and * system counter from the device driver + * @ctx: Context passed to get_time_fn() + * @history_begin: Historical reference point used to interpolate system + * time when counter provided by the driver is before the current interval * @xtstamp: Receives simultaneously captured system and device time * * Reads a timestamp from a device and correlates it to system time @@ -920,13 +1036,18 @@ int get_device_system_crosststamp(int (*get_time_fn) struct system_counterval_t *sys_counterval, void *ctx), void *ctx, + struct system_time_snapshot *history_begin, struct system_device_crosststamp *xtstamp) { struct system_counterval_t system_counterval; struct timekeeper *tk = &tk_core.timekeeper; + cycle_t cycles, now, interval_start; + unsigned int clock_was_set_seq; ktime_t base_real, base_raw; s64 nsec_real, nsec_raw; + u8 cs_was_changed_seq; unsigned long seq; + bool do_interp; int ret; do { @@ -946,6 +1067,22 @@ int get_device_system_crosststamp(int (*get_time_fn) */ if (tk->tkr_mono.clock != system_counterval.cs) return -ENODEV; + cycles = system_counterval.cycles; + + /* + * Check whether the system counter value provided by the + * device driver is on the current timekeeping interval. + */ + now = tk->tkr_mono.read(tk->tkr_mono.clock); + interval_start = tk->tkr_mono.cycle_last; + if (!cycle_between(interval_start, cycles, now)) { + clock_was_set_seq = tk->clock_was_set_seq; + cs_was_changed_seq = tk->cs_was_changed_seq; + cycles = interval_start; + do_interp = true; + } else { + do_interp = false; + } base_real = ktime_add(tk->tkr_mono.base, tk_core.timekeeper.offs_real); @@ -959,6 +1096,38 @@ int get_device_system_crosststamp(int (*get_time_fn) xtstamp->sys_realtime = ktime_add_ns(base_real, nsec_real); xtstamp->sys_monoraw = ktime_add_ns(base_raw, nsec_raw); + + /* + * Interpolate if necessary, adjusting back from the start of the + * current interval + */ + if (do_interp) { + cycle_t partial_history_cycles, total_history_cycles; + bool discontinuity; + + /* + * Check that the counter value occurs after the provided + * history reference and that the history doesn't cross a + * clocksource change + */ + if (!history_begin || + !cycle_between(history_begin->cycles, + system_counterval.cycles, cycles) || + history_begin->cs_was_changed_seq != cs_was_changed_seq) + return -EINVAL; + partial_history_cycles = cycles - system_counterval.cycles; + total_history_cycles = cycles - history_begin->cycles; + discontinuity = + history_begin->clock_was_set_seq != clock_was_set_seq; + + ret = adjust_historical_crosststamp(history_begin, + partial_history_cycles, + total_history_cycles, + discontinuity, xtstamp); + if (ret) + return ret; + } + return 0; } EXPORT_SYMBOL_GPL(get_device_system_crosststamp); |