1 files changed, 410 insertions, 15 deletions

diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index d2321891538f..5c00242fa921 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -14,6 +14,7 @@
 #include <linux/timex.h>
 #include <linux/time.h>
 #include <linux/mm.h>
+#include <linux/module.h>
 
 /*
  * NTP timekeeping variables:
@@ -74,6 +75,162 @@ static long			time_adjust;
 /* constant (boot-param configurable) NTP tick adjustment (upscaled)    */
 static s64                      ntp_tick_adj;
 
+#ifdef CONFIG_NTP_PPS
+
+/*
+ * The following variables are used when a pulse-per-second (PPS) signal
+ * is available. They establish the engineering parameters of the clock
+ * discipline loop when controlled by the PPS signal.
+ */
+#define PPS_VALID       10      /* PPS signal watchdog max (s) */
+#define PPS_POPCORN     4       /* popcorn spike threshold (shift) */
+#define PPS_INTMIN      2       /* min freq interval (s) (shift) */
+#define PPS_INTMAX      8       /* max freq interval (s) (shift) */
+#define PPS_INTCOUNT    4       /* number of consecutive good intervals to
+                                   increase pps_shift or consecutive bad
+                                   intervals to decrease it */
+#define PPS_MAXWANDER   100000  /* max PPS freq wander (ns/s) */
+
+static int pps_valid;           /* signal watchdog counter */
+static long pps_tf[3];          /* phase median filter */
+static long pps_jitter;         /* current jitter (ns) */
+static struct timespec pps_fbase; /* beginning of the last freq interval */
+static int pps_shift;           /* current interval duration (s) (shift) */
+static int pps_intcnt;          /* interval counter */
+static s64 pps_freq;            /* frequency offset (scaled ns/s) */
+static long pps_stabil;         /* current stability (scaled ns/s) */
+
+/*
+ * PPS signal quality monitors
+ */
+static long pps_calcnt;         /* calibration intervals */
+static long pps_jitcnt;         /* jitter limit exceeded */
+static long pps_stbcnt;         /* stability limit exceeded */
+static long pps_errcnt;         /* calibration errors */
+
+
+/* PPS kernel consumer compensates the whole phase error immediately.
+ * Otherwise, reduce the offset by a fixed factor times the time constant.
+ */
+static inline s64 ntp_offset_chunk(s64 offset)
+{
+        if (time_status & STA_PPSTIME && time_status & STA_PPSSIGNAL)
+                return offset;
+        else
+                return shift_right(offset, SHIFT_PLL + time_constant);
+}
+
+static inline void pps_reset_freq_interval(void)
+{
+        /* the PPS calibration interval may end
+           surprisingly early */
+        pps_shift = PPS_INTMIN;
+        pps_intcnt = 0;
+}
+
+/**
+ * pps_clear - Clears the PPS state variables
+ *
+ * Must be called while holding a write on the xtime_lock
+ */
+static inline void pps_clear(void)
+{
+        pps_reset_freq_interval();
+        pps_tf[0] = 0;
+        pps_tf[1] = 0;
+        pps_tf[2] = 0;
+        pps_fbase.tv_sec = pps_fbase.tv_nsec = 0;
+        pps_freq = 0;
+}
+
+/* Decrease pps_valid to indicate that another second has passed since
+ * the last PPS signal. When it reaches 0, indicate that PPS signal is
+ * missing.
+ *
+ * Must be called while holding a write on the xtime_lock
+ */
+static inline void pps_dec_valid(void)
+{
+        if (pps_valid > 0)
+                pps_valid--;
+        else {
+                time_status &= ~(STA_PPSSIGNAL | STA_PPSJITTER |
+                                 STA_PPSWANDER | STA_PPSERROR);
+                pps_clear();
+        }
+}
+
+static inline void pps_set_freq(s64 freq)
+{
+        pps_freq = freq;
+}
+
+static inline int is_error_status(int status)
+{
+        return (time_status & (STA_UNSYNC|STA_CLOCKERR))
+                /* PPS signal lost when either PPS time or
+                 * PPS frequency synchronization requested
+                 */
+                || ((time_status & (STA_PPSFREQ|STA_PPSTIME))
+                        && !(time_status & STA_PPSSIGNAL))
+                /* PPS jitter exceeded when
+                 * PPS time synchronization requested */
+                || ((time_status & (STA_PPSTIME|STA_PPSJITTER))
+                        == (STA_PPSTIME|STA_PPSJITTER))
+                /* PPS wander exceeded or calibration error when
+                 * PPS frequency synchronization requested
+                 */
+                || ((time_status & STA_PPSFREQ)
+                        && (time_status & (STA_PPSWANDER|STA_PPSERROR)));
+}
+
+static inline void pps_fill_timex(struct timex *txc)
+{
+        txc->ppsfreq       = shift_right((pps_freq >> PPM_SCALE_INV_SHIFT) *
+                                         PPM_SCALE_INV, NTP_SCALE_SHIFT);
+        txc->jitter        = pps_jitter;
+        if (!(time_status & STA_NANO))
+                txc->jitter /= NSEC_PER_USEC;
+        txc->shift         = pps_shift;
+        txc->stabil        = pps_stabil;
+        txc->jitcnt        = pps_jitcnt;
+        txc->calcnt        = pps_calcnt;
+        txc->errcnt        = pps_errcnt;
+        txc->stbcnt        = pps_stbcnt;
+}
+
+#else /* !CONFIG_NTP_PPS */
+
+static inline s64 ntp_offset_chunk(s64 offset)
+{
+        return shift_right(offset, SHIFT_PLL + time_constant);
+}
+
+static inline void pps_reset_freq_interval(void) {}
+static inline void pps_clear(void) {}
+static inline void pps_dec_valid(void) {}
+static inline void pps_set_freq(s64 freq) {}
+
+static inline int is_error_status(int status)
+{
+        return status & (STA_UNSYNC|STA_CLOCKERR);
+}
+
+static inline void pps_fill_timex(struct timex *txc)
+{
+        /* PPS is not implemented, so these are zero */
+        txc->ppsfreq       = 0;
+        txc->jitter        = 0;
+        txc->shift         = 0;
+        txc->stabil        = 0;
+        txc->jitcnt        = 0;
+        txc->calcnt        = 0;
+        txc->errcnt        = 0;
+        txc->stbcnt        = 0;
+}
+
+#endif /* CONFIG_NTP_PPS */
+
 /*
  * NTP methods:
  */
@@ -185,6 +342,9 @@ void ntp_clear(void)
 
         tick_length     = tick_length_base;
         time_offset     = 0;
+
+        /* Clear PPS state variables */
+        pps_clear();
 }
 
 /*
@@ -250,16 +410,16 @@ void second_overflow(void)
                 time_status |= STA_UNSYNC;
         }
 
-        /*
-         * Compute the phase adjustment for the next second. The offset is
-         * reduced by a fixed factor times the time constant.
-         */
+        /* Compute the phase adjustment for the next second */
         tick_length      = tick_length_base;
 
-        delta            = shift_right(time_offset, SHIFT_PLL + time_constant);
+        delta            = ntp_offset_chunk(time_offset);
         time_offset     -= delta;
         tick_length     += delta;
 
+        /* Check PPS signal */
+        pps_dec_valid();
+
         if (!time_adjust)
                 return;
 
@@ -369,6 +529,8 @@ static inline void process_adj_status(struct timex *txc, struct timespec *ts)
         if ((time_status & STA_PLL) && !(txc->status & STA_PLL)) {
                 time_state = TIME_OK;
                 time_status = STA_UNSYNC;
+                /* restart PPS frequency calibration */
+                pps_reset_freq_interval();
         }
 
         /*
@@ -418,6 +580,8 @@ static inline void process_adjtimex_modes(struct timex *txc, struct timespec *ts
                 time_freq = txc->freq * PPM_SCALE;
                 time_freq = min(time_freq, MAXFREQ_SCALED);
                 time_freq = max(time_freq, -MAXFREQ_SCALED);
+                /* update pps_freq */
+                pps_set_freq(time_freq);
         }
 
         if (txc->modes & ADJ_MAXERROR)
@@ -508,7 +672,8 @@ int do_adjtimex(struct timex *txc)
         }
 
         result = time_state;    /* mostly `TIME_OK' */
-        if (time_status & (STA_UNSYNC|STA_CLOCKERR))
+        /* check for errors */
+        if (is_error_status(time_status))
                 result = TIME_ERROR;
 
         txc->freq          = shift_right((time_freq >> PPM_SCALE_INV_SHIFT) *
@@ -522,15 +687,8 @@ int do_adjtimex(struct timex *txc)
         txc->tick          = tick_usec;
         txc->tai           = time_tai;
 
-        /* PPS is not implemented, so these are zero */
-        txc->ppsfreq       = 0;
-        txc->jitter        = 0;
-        txc->shift         = 0;
-        txc->stabil        = 0;
-        txc->jitcnt        = 0;
-        txc->calcnt        = 0;
-        txc->errcnt        = 0;
-        txc->stbcnt        = 0;
+        /* fill PPS status fields */
+        pps_fill_timex(txc);
 
         write_sequnlock_irq(&xtime_lock);
 
@@ -544,6 +702,243 @@ int do_adjtimex(struct timex *txc)
         return result;
 }
 
+#ifdef  CONFIG_NTP_PPS
+
+/* actually struct pps_normtime is good old struct timespec, but it is
+ * semantically different (and it is the reason why it was invented):
+ * pps_normtime.nsec has a range of ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ]
+ * while timespec.tv_nsec has a range of [0, NSEC_PER_SEC) */
+struct pps_normtime {
+        __kernel_time_t sec;    /* seconds */
+        long            nsec;   /* nanoseconds */
+};
+
+/* normalize the timestamp so that nsec is in the
+   ( -NSEC_PER_SEC / 2, NSEC_PER_SEC / 2 ] interval */
+static inline struct pps_normtime pps_normalize_ts(struct timespec ts)
+{
+        struct pps_normtime norm = {
+                .sec = ts.tv_sec,
+                .nsec = ts.tv_nsec
+        };
+
+        if (norm.nsec > (NSEC_PER_SEC >> 1)) {
+                norm.nsec -= NSEC_PER_SEC;
+                norm.sec++;
+        }
+
+        return norm;
+}
+
+/* get current phase correction and jitter */
+static inline long pps_phase_filter_get(long *jitter)
+{
+        *jitter = pps_tf[0] - pps_tf[1];
+        if (*jitter < 0)
+                *jitter = -*jitter;
+
+        /* TODO: test various filters */
+        return pps_tf[0];
+}
+
+/* add the sample to the phase filter */
+static inline void pps_phase_filter_add(long err)
+{
+        pps_tf[2] = pps_tf[1];
+        pps_tf[1] = pps_tf[0];
+        pps_tf[0] = err;
+}
+
+/* decrease frequency calibration interval length.
+ * It is halved after four consecutive unstable intervals.
+ */
+static inline void pps_dec_freq_interval(void)
+{
+        if (--pps_intcnt <= -PPS_INTCOUNT) {
+                pps_intcnt = -PPS_INTCOUNT;
+                if (pps_shift > PPS_INTMIN) {
+                        pps_shift--;
+                        pps_intcnt = 0;
+                }
+        }
+}
+
+/* increase frequency calibration interval length.
+ * It is doubled after four consecutive stable intervals.
+ */
+static inline void pps_inc_freq_interval(void)
+{
+        if (++pps_intcnt >= PPS_INTCOUNT) {
+                pps_intcnt = PPS_INTCOUNT;
+                if (pps_shift < PPS_INTMAX) {
+                        pps_shift++;
+                        pps_intcnt = 0;
+                }
+        }
+}
+
+/* update clock frequency based on MONOTONIC_RAW clock PPS signal
+ * timestamps
+ *
+ * At the end of the calibration interval the difference between the
+ * first and last MONOTONIC_RAW clock timestamps divided by the length
+ * of the interval becomes the frequency update. If the interval was
+ * too long, the data are discarded.
+ * Returns the difference between old and new frequency values.
+ */
+static long hardpps_update_freq(struct pps_normtime freq_norm)
+{
+        long delta, delta_mod;
+        s64 ftemp;
+
+        /* check if the frequency interval was too long */
+        if (freq_norm.sec > (2 << pps_shift)) {
+                time_status |= STA_PPSERROR;
+                pps_errcnt++;
+                pps_dec_freq_interval();
+                pr_err("hardpps: PPSERROR: interval too long - %ld s\n",
+                                freq_norm.sec);
+                return 0;
+        }
+
+        /* here the raw frequency offset and wander (stability) is
+         * calculated. If the wander is less than the wander threshold
+         * the interval is increased; otherwise it is decreased.
+         */
+        ftemp = div_s64(((s64)(-freq_norm.nsec)) << NTP_SCALE_SHIFT,
+                        freq_norm.sec);
+        delta = shift_right(ftemp - pps_freq, NTP_SCALE_SHIFT);
+        pps_freq = ftemp;
+        if (delta > PPS_MAXWANDER || delta < -PPS_MAXWANDER) {
+                pr_warning("hardpps: PPSWANDER: change=%ld\n", delta);
+                time_status |= STA_PPSWANDER;
+                pps_stbcnt++;
+                pps_dec_freq_interval();
+        } else {        /* good sample */
+                pps_inc_freq_interval();
+        }
+
+        /* the stability metric is calculated as the average of recent
+         * frequency changes, but is used only for performance
+         * monitoring
+         */
+        delta_mod = delta;
+        if (delta_mod < 0)
+                delta_mod = -delta_mod;
+        pps_stabil += (div_s64(((s64)delta_mod) <<
+                                (NTP_SCALE_SHIFT - SHIFT_USEC),
+                                NSEC_PER_USEC) - pps_stabil) >> PPS_INTMIN;
+
+        /* if enabled, the system clock frequency is updated */
+        if ((time_status & STA_PPSFREQ) != 0 &&
+            (time_status & STA_FREQHOLD) == 0) {
+                time_freq = pps_freq;
+                ntp_update_frequency();
+        }
+
+        return delta;
+}
+
+/* correct REALTIME clock phase error against PPS signal */
+static void hardpps_update_phase(long error)
+{
+        long correction = -error;
+        long jitter;
+
+        /* add the sample to the median filter */
+        pps_phase_filter_add(correction);
+        correction = pps_phase_filter_get(&jitter);
+
+        /* Nominal jitter is due to PPS signal noise. If it exceeds the
+         * threshold, the sample is discarded; otherwise, if so enabled,
+         * the time offset is updated.
+         */
+        if (jitter > (pps_jitter << PPS_POPCORN)) {
+                pr_warning("hardpps: PPSJITTER: jitter=%ld, limit=%ld\n",
+                       jitter, (pps_jitter << PPS_POPCORN));
+                time_status |= STA_PPSJITTER;
+                pps_jitcnt++;
+        } else if (time_status & STA_PPSTIME) {
+                /* correct the time using the phase offset */
+                time_offset = div_s64(((s64)correction) << NTP_SCALE_SHIFT,
+                                NTP_INTERVAL_FREQ);
+                /* cancel running adjtime() */
+                time_adjust = 0;
+        }
+        /* update jitter */
+        pps_jitter += (jitter - pps_jitter) >> PPS_INTMIN;
+}
+
+/*
+ * hardpps() - discipline CPU clock oscillator to external PPS signal
+ *
+ * This routine is called at each PPS signal arrival in order to
+ * discipline the CPU clock oscillator to the PPS signal. It takes two
+ * parameters: REALTIME and MONOTONIC_RAW clock timestamps. The former
+ * is used to correct clock phase error and the latter is used to
+ * correct the frequency.
+ *
+ * This code is based on David Mills's reference nanokernel
+ * implementation. It was mostly rewritten but keeps the same idea.
+ */
+void hardpps(const struct timespec *phase_ts, const struct timespec *raw_ts)
+{
+        struct pps_normtime pts_norm, freq_norm;
+        unsigned long flags;
+
+        pts_norm = pps_normalize_ts(*phase_ts);
+
+        write_seqlock_irqsave(&xtime_lock, flags);
+
+        /* clear the error bits, they will be set again if needed */
+        time_status &= ~(STA_PPSJITTER | STA_PPSWANDER | STA_PPSERROR);
+
+        /* indicate signal presence */
+        time_status |= STA_PPSSIGNAL;
+        pps_valid = PPS_VALID;
+
+        /* when called for the first time,
+         * just start the frequency interval */
+        if (unlikely(pps_fbase.tv_sec == 0)) {
+                pps_fbase = *raw_ts;
+                write_sequnlock_irqrestore(&xtime_lock, flags);
+                return;
+        }
+
+        /* ok, now we have a base for frequency calculation */
+        freq_norm = pps_normalize_ts(timespec_sub(*raw_ts, pps_fbase));
+
+        /* check that the signal is in the range
+         * [1s - MAXFREQ us, 1s + MAXFREQ us], otherwise reject it */
+        if ((freq_norm.sec == 0) ||
+                        (freq_norm.nsec > MAXFREQ * freq_norm.sec) ||
+                        (freq_norm.nsec < -MAXFREQ * freq_norm.sec)) {
+                time_status |= STA_PPSJITTER;
+                /* restart the frequency calibration interval */
+                pps_fbase = *raw_ts;
+                write_sequnlock_irqrestore(&xtime_lock, flags);
+                pr_err("hardpps: PPSJITTER: bad pulse\n");
+                return;
+        }
+
+        /* signal is ok */
+
+        /* check if the current frequency interval is finished */
+        if (freq_norm.sec >= (1 << pps_shift)) {
+                pps_calcnt++;
+                /* restart the frequency calibration interval */
+                pps_fbase = *raw_ts;
+                hardpps_update_freq(freq_norm);
+        }
+
+        hardpps_update_phase(pts_norm.nsec);
+
+        write_sequnlock_irqrestore(&xtime_lock, flags);
+}
+EXPORT_SYMBOL(hardpps);
+
+#endif  /* CONFIG_NTP_PPS */
+
 static int __init ntp_tick_adj_setup(char *str)
 {
         ntp_tick_adj = simple_strtol(str, NULL, 0);