[PATCH v6 0/9] Patchset enabling hardware based cross-timestamps for next gen Intel platforms

@@ -298,13 +298,11 @@ u32 (*arch_gettimeoffset)(void) = default_arch_gettimeoffset;
 static inline u32 arch_gettimeoffset(void) { return 0; }
 #endif
 
-static inline s64 timekeeping_get_ns(struct tk_read_base *tkr)
+static inline s64 timekeeping_delta_to_ns(struct tk_read_base *tkr,
+					  cycle_t delta)
 {
-	cycle_t delta;
 	s64 nsec;
 
-	delta = timekeeping_get_delta(tkr);
-
 	nsec = delta * tkr->mult + tkr->xtime_nsec;
 	nsec >>= tkr->shift;
 

@@ -312,6 +310,24 @@ static inline s64 timekeeping_get_ns(struct tk_read_base *tkr)
 	return nsec + arch_gettimeoffset();
 }
 
+static inline s64 timekeeping_get_ns(struct tk_read_base *tkr)
+{
+	cycle_t delta;
+
+	delta = timekeeping_get_delta(tkr);
+	return timekeeping_delta_to_ns(tkr, delta);
+}
+
+static inline s64 timekeeping_cycles_to_ns(struct tk_read_base *tkr,
+					    cycle_t cycles)
+{
+	cycle_t delta;
+
+	/* calculate the delta since the last update_wall_time */
+	delta = clocksource_delta(cycles, tkr->cycle_last, tkr->mask);
+	return timekeeping_delta_to_ns(tkr, delta);
+}
+
 /**
  * update_fast_timekeeper - Update the fast and NMI safe monotonic timekeeper.
  * @tkr: Timekeeping readout base from which we take the update

@@ -281,4 +281,17 @@ struct correlated_cs {
 					   cycle_t cycles);
 };
 
+/*
+ * struct system_time_snapshot - simultaneous raw/real time capture with
+ *	counter value
+ * @cycles:	Clocksource counter value to produce the system times
+ * @real:	Realtime system time
+ * @raw:	Monotonic raw system time
+ */
+struct system_time_snapshot {
+	cycles_t	cycles;
+	ktime_t		real;
+	ktime_t		raw;
+};
+
 #endif /* _LINUX_CLOCKSOURCE_H */

@@ -301,6 +301,12 @@ struct sync_device_time_cb {
 extern int get_device_system_crosststamp(struct sync_device_time_cb *cb,
 					 struct system_device_crosststamp *ts);
 
+struct system_time_snapshot;
+/*
+ * Simultaneously snapshot realtime and monotonic raw clocks
+ */
+extern void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot);
+
 /*
  * Persistent clock related interfaces
  */

@@ -862,6 +862,37 @@ time64_t ktime_get_real_seconds(void)
 }
 EXPORT_SYMBOL_GPL(ktime_get_real_seconds);
 
+/**
+ * ktime_get_snapshot - snapshots the realtime/monotonic raw clocks with counter
+ * @systime_snapshot:	pointer to struct receiving the system time snapshot
+ */
+void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot)
+{
+	struct timekeeper *tk = &tk_core.timekeeper;
+	unsigned long seq;
+	ktime_t base_raw;
+	ktime_t base_real;
+	s64 nsec_raw;
+	s64 nsec_real;
+	cycle_t now;
+
+	do {
+		seq = read_seqcount_begin(&tk_core.seq);
+
+		now = tk->tkr_mono.read(tk->tkr_mono.clock);
+		base_real = ktime_add(tk->tkr_mono.base,
+				      tk_core.timekeeper.offs_real);
+		base_raw = tk->tkr_raw.base;
+		nsec_real = timekeeping_cycles_to_ns(&tk->tkr_mono, now);
+		nsec_raw  = timekeeping_cycles_to_ns(&tk->tkr_raw, now);
+	} while (read_seqcount_retry(&tk_core.seq, seq));
+
+	systime_snapshot->cycles = now;
+	systime_snapshot->real = ktime_add_ns(base_real, nsec_real);
+	systime_snapshot->raw = ktime_add_ns(base_raw, nsec_raw);
+}
+EXPORT_SYMBOL_GPL(ktime_get_snapshot);
+
 #ifdef CONFIG_NTP_PPS
 
 /**

@@ -83,6 +83,15 @@ config E1000E
 	  To compile this driver as a module, choose M here. The module
 	  will be called e1000e.
 
+config E1000E_HWTS
+	bool "Support HW cross-timestamp on PCH devices"
+	default y
+	depends on E1000E && X86
+	---help---
+	 Say Y to enable hardware supported cross-timestamping on PCH
+	 devices. The cross-timestamp is available through the PTP clock
+	 driver precise cross-timestamp ioctl (PTP_SYS_OFFSET_PRECISE).
+
 config IGB
 	tristate "Intel(R) 82575/82576 PCI-Express Gigabit Ethernet support"
 	depends on PCI

@@ -527,6 +527,11 @@
 #define E1000_RXCW_C          0x20000000        /* Receive config */
 #define E1000_RXCW_SYNCH      0x40000000        /* Receive config synch */
 
+/* HH Time Sync */
+#define E1000_TSYNCTXCTL_MAX_ALLOWED_DLY_MASK	0x0000F000 /* max delay */
+#define E1000_TSYNCTXCTL_SYNC_COMP		0x40000000 /* sync complete */
+#define E1000_TSYNCTXCTL_START_SYNC		0x80000000 /* initiate sync */
+
 #define E1000_TSYNCTXCTL_VALID		0x00000001 /* Tx timestamp valid */
 #define E1000_TSYNCTXCTL_ENABLED	0x00000010 /* enable Tx timestamping */
 

@@ -26,6 +26,11 @@
 
 #include "e1000.h"
 
+#ifdef CONFIG_E1000E_HWTS
+#include <asm/tsc.h>
+#include <linux/ktime.h>
+#endif
+
 /**
  * e1000e_phc_adjfreq - adjust the frequency of the hardware clock
  * @ptp: ptp clock structure

@@ -98,6 +103,82 @@ static int e1000e_phc_adjtime(struct ptp_clock_info *ptp, s64 delta)
 	return 0;
 }
 
+#ifdef CONFIG_E1000E_HWTS
+#define MAX_HW_WAIT_COUNT (3)
+
+/**
+ * e1000e_phc_get_syncdevicetime - Callback given to timekeeping code reads system/device registers
+ * @device: current device time
+ * @system: system counter value read synchronously with device time
+ * @ctx: context provided by timekeeping code
+ *
+ * Read device and system (ART) clock simultaneously and return the corrected
+ * clock values in ns.
+ **/
+static int e1000e_phc_get_syncdevicetime(ktime_t *device,
+					 struct system_counterval_t *system,
+					 void *ctx)
+{
+	struct e1000_adapter *adapter = (struct e1000_adapter *)ctx;
+	struct e1000_hw *hw = &adapter->hw;
+	unsigned long flags;
+	int i;
+	u32 tsync_ctrl;
+	cycle_t dev_cycles;
+
+	tsync_ctrl = er32(TSYNCTXCTL);
+	tsync_ctrl |= E1000_TSYNCTXCTL_START_SYNC |
+		E1000_TSYNCTXCTL_MAX_ALLOWED_DLY_MASK;
+	ew32(TSYNCTXCTL, tsync_ctrl);
+	for (i = 0; i < MAX_HW_WAIT_COUNT; ++i) {
+		udelay(1);
+		tsync_ctrl = er32(TSYNCTXCTL);
+		if (tsync_ctrl & E1000_TSYNCTXCTL_SYNC_COMP)
+			break;
+	}
+
+	if (i == MAX_HW_WAIT_COUNT)
+		return -ETIMEDOUT;
+
+	dev_cycles = er32(SYSSTMPH);
+	dev_cycles <<= 32;
+	dev_cycles |= er32(SYSSTMPL);
+	spin_lock_irqsave(&adapter->systim_lock, flags);
+	*device = ns_to_ktime(timecounter_cyc2time(&adapter->tc, dev_cycles));
+	spin_unlock_irqrestore(&adapter->systim_lock, flags);
+
+	system->cycles = er32(PLTSTMPH);
+	system->cycles <<= 32;
+	system->cycles |= er32(PLTSTMPL);
+	system->cs = art_timestamper.related_cs;
+	system->cycles = art_timestamper.convert(&art_timestamper,
+						 system->cycles);
+	return 0;
+}
+
+/**
+ * e1000e_phc_getsynctime - Reads the current system/device cross timestamp
+ * @ptp: ptp clock structure
+ * @cts: structure containing timestamp
+ *
+ * Read device and system (ART) clock simultaneously and return the scaled
+ * clock values in ns.
+ **/
+static int e1000e_phc_getcrosststamp(struct ptp_clock_info *ptp,
+				     struct system_device_crosststamp *xtstamp)
+{
+	struct e1000_adapter *adapter = container_of(ptp, struct e1000_adapter,
+						     ptp_clock_info);
+	struct sync_device_time_cb sync_devicetime;
+	int ret;
+
+	sync_devicetime.get_time = e1000e_phc_get_syncdevicetime;
+	sync_devicetime.ctx = adapter;
+	ret = get_device_system_crosststamp(&sync_devicetime, NULL, xtstamp);
+	return ret;
+}
+#endif/*CONFIG_E1000E_HWTS*/
+
 /**
  * e1000e_phc_gettime - Reads the current time from the hardware clock
  * @ptp: ptp clock structure

@@ -236,6 +317,13 @@ void e1000e_ptp_init(struct e1000_adapter *adapter)
 		break;
 	}
 
+#ifdef CONFIG_E1000E_HWTS
+	/* CPU must have ART and GBe must be from Sunrise Point or greater */
+	if (hw->mac.type >= e1000_pch_spt && boot_cpu_has(X86_FEATURE_ART))
+		adapter->ptp_clock_info.getcrosststamp =
+			e1000e_phc_getcrosststamp;
+#endif/*CONFIG_E1000E_HWTS*/
+
 	INIT_DELAYED_WORK(&adapter->systim_overflow_work,
 			  e1000e_systim_overflow_work);
 

@@ -245,6 +245,10 @@
 #define E1000_SYSTIML	0x0B600	/* System time register Low - RO */
 #define E1000_SYSTIMH	0x0B604	/* System time register High - RO */
 #define E1000_TIMINCA	0x0B608	/* Increment attributes register - RW */
+#define E1000_SYSSTMPL  0x0B648 /* HH Timesync system stamp low register */
+#define E1000_SYSSTMPH  0x0B64C /* HH Timesync system stamp hi register */
+#define E1000_PLTSTMPL  0x0B640 /* HH Timesync platform stamp low register */
+#define E1000_PLTSTMPH  0x0B644 /* HH Timesync platform stamp hi register */
 #define E1000_RXMTRL	0x0B634	/* Time sync Rx EtherType and Msg Type - RW */
 #define E1000_RXUDP	0x0B638	/* Time Sync Rx UDP Port - RW */
 

@@ -277,13 +277,15 @@ int main(int argc, char *argv[])
 			       "  %d external time stamp channels\n"
 			       "  %d programmable periodic signals\n"
 			       "  %d pulse per second\n"
-			       "  %d programmable pins\n",
+			       "  %d programmable pins\n"
+			       "  %d cross timestamping\n",
 			       caps.max_adj,
 			       caps.n_alarm,
 			       caps.n_ext_ts,
 			       caps.n_per_out,
 			       caps.pps,
-			       caps.n_pins);
+			       caps.n_pins,
+			       caps.cross_timestamping);
 		}
 	}
 

@@ -22,6 +22,7 @@
 #include <linux/poll.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
+#include <linux/timekeeping.h>
 
 #include "ptp_private.h"
 

@@ -120,11 +121,13 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
 	struct ptp_clock_caps caps;
 	struct ptp_clock_request req;
 	struct ptp_sys_offset *sysoff = NULL;
+	struct ptp_sys_offset_precise precise_offset;
 	struct ptp_pin_desc pd;
 	struct ptp_clock *ptp = container_of(pc, struct ptp_clock, clock);
 	struct ptp_clock_info *ops = ptp->info;
 	struct ptp_clock_time *pct;
 	struct timespec64 ts;
+	struct system_device_crosststamp xtstamp;
 	int enable, err = 0;
 	unsigned int i, pin_index;
 

@@ -138,6 +141,7 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
 		caps.n_per_out = ptp->info->n_per_out;
 		caps.pps = ptp->info->pps;
 		caps.n_pins = ptp->info->n_pins;
+		caps.cross_timestamping = ptp->info->getcrosststamp != NULL;
 		if (copy_to_user((void __user *)arg, &caps, sizeof(caps)))
 			err = -EFAULT;
 		break;

@@ -180,6 +184,29 @@ long ptp_ioctl(struct posix_clock *pc, unsigned int cmd, unsigned long arg)
 		err = ops->enable(ops, &req, enable);
 		break;
 
+	case PTP_SYS_OFFSET_PRECISE:
+		if (!ptp->info->getcrosststamp) {
+			err = -EOPNOTSUPP;
+			break;
+		}
+		err = ptp->info->getcrosststamp(ptp->info, &xtstamp);
+		if (err)
+			break;
+
+		ts = ktime_to_timespec64(xtstamp.device);
+		precise_offset.device.sec = ts.tv_sec;
+		precise_offset.device.nsec = ts.tv_nsec;
+		ts = ktime_to_timespec64(xtstamp.sys_realtime);
+		precise_offset.sys_realtime.sec = ts.tv_sec;
+		precise_offset.sys_realtime.nsec = ts.tv_nsec;
+		ts = ktime_to_timespec64(xtstamp.sys_monoraw);
+		precise_offset.sys_monoraw.sec = ts.tv_sec;
+		precise_offset.sys_monoraw.nsec = ts.tv_nsec;
+		if (copy_to_user((void __user *)arg, &precise_offset,
+				 sizeof(precise_offset)))
+			err = -EFAULT;
+		break;
+
 	case PTP_SYS_OFFSET:
 		sysoff = kmalloc(sizeof(*sysoff), GFP_KERNEL);
 		if (!sysoff) {

@@ -38,6 +38,7 @@ struct ptp_clock_request {
 	};
 };
 
+struct system_device_crosststamp;
 /**
  * struct ptp_clock_info - decribes a PTP hardware clock
  *

@@ -67,6 +68,11 @@ struct ptp_clock_request {
  * @gettime64:  Reads the current time from the hardware clock.
  *              parameter ts: Holds the result.
  *
+ * @getcrosststamp:  Reads the current time from the hardware clock and
+ *                   system clock simultaneously.
+ *                   parameter cts: Contains timestamp (device,system) pair,
+ *                   where system time is realtime and monotonic.
+ *
  * @settime64:  Set the current time on the hardware clock.
  *              parameter ts: Time value to set.
  *

@@ -105,6 +111,8 @@ struct ptp_clock_info {
 	int (*adjfreq)(struct ptp_clock_info *ptp, s32 delta);
 	int (*adjtime)(struct ptp_clock_info *ptp, s64 delta);
 	int (*gettime64)(struct ptp_clock_info *ptp, struct timespec64 *ts);
+	int (*getcrosststamp)(struct ptp_clock_info *ptp,
+			      struct system_device_crosststamp *cts);
 	int (*settime64)(struct ptp_clock_info *p, const struct timespec64 *ts);
 	int (*enable)(struct ptp_clock_info *ptp,
 		      struct ptp_clock_request *request, int on);

@@ -51,7 +51,9 @@ struct ptp_clock_caps {
 	int n_per_out; /* Number of programmable periodic signals. */
 	int pps;       /* Whether the clock supports a PPS callback. */
 	int n_pins;    /* Number of input/output pins. */
-	int rsv[14];   /* Reserved for future use. */
+	/* Whether the clock supports precise system-device cross timestamps */
+	int cross_timestamping;
+	int rsv[13];   /* Reserved for future use. */
 };
 
 struct ptp_extts_request {

@@ -81,6 +83,13 @@ struct ptp_sys_offset {
 	struct ptp_clock_time ts[2 * PTP_MAX_SAMPLES + 1];
 };
 
+struct ptp_sys_offset_precise {
+	struct ptp_clock_time device;
+	struct ptp_clock_time sys_realtime;
+	struct ptp_clock_time sys_monoraw;
+	unsigned int rsv[4];    /* Reserved for future use. */
+};
+
 enum ptp_pin_function {
 	PTP_PF_NONE,
 	PTP_PF_EXTTS,

@@ -124,6 +133,8 @@ struct ptp_pin_desc {
 #define PTP_SYS_OFFSET     _IOW(PTP_CLK_MAGIC, 5, struct ptp_sys_offset)
 #define PTP_PIN_GETFUNC    _IOWR(PTP_CLK_MAGIC, 6, struct ptp_pin_desc)
 #define PTP_PIN_SETFUNC    _IOW(PTP_CLK_MAGIC, 7, struct ptp_pin_desc)
+#define PTP_SYS_OFFSET_PRECISE \
+	_IOWR(PTP_CLK_MAGIC, 8, struct ptp_sys_offset_precise)
 
 struct ptp_extts_event {
 	struct ptp_clock_time t; /* Time event occured. */

@@ -111,22 +111,17 @@ static inline void timespec_to_pps_ktime(struct pps_ktime *kt,
 	kt->nsec = ts.tv_nsec;
 }
 
-#ifdef CONFIG_NTP_PPS
-
 static inline void pps_get_ts(struct pps_event_time *ts)
 {
-	ktime_get_raw_and_real_ts64(&ts->ts_raw, &ts->ts_real);
-}
+	struct system_time_snapshot snap;
 
-#else /* CONFIG_NTP_PPS */
-
-static inline void pps_get_ts(struct pps_event_time *ts)
-{
-	ktime_get_real_ts64(&ts->ts_real);
+	ktime_get_snapshot(&snap);
+	ts->ts_real = ktime_to_timespec64(snap.real);
+#ifdef CONFIG_NTP_PPS
+	ts->ts_raw = ktime_to_timespec64(snap.raw);
+#endif
 }
 
-#endif /* CONFIG_NTP_PPS */
-
 /* Subtract known time delay from PPS event time(s) */
 static inline void pps_sub_ts(struct pps_event_time *ts, struct timespec64 delta)
 {

@@ -877,6 +877,8 @@ void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot)
 	s64 nsec_real;
 	cycle_t now;
 
+	WARN_ON(timekeeping_suspended);
+
 	do {
 		seq = read_seqcount_begin(&tk_core.seq);
 

@@ -896,44 +898,6 @@ void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot)
 }
 EXPORT_SYMBOL_GPL(ktime_get_snapshot);
 
-#ifdef CONFIG_NTP_PPS
-
-/**
- * ktime_get_raw_and_real_ts64 - get day and raw monotonic time in timespec format
- * @ts_raw:	pointer to the timespec to be set to raw monotonic time
- * @ts_real:	pointer to the timespec to be set to the time of day
- *
- * This function reads both the time of day and raw monotonic time at the
- * same time atomically and stores the resulting timestamps in timespec
- * format.
- */
-void ktime_get_raw_and_real_ts64(struct timespec64 *ts_raw, struct timespec64 *ts_real)
-{
-	struct timekeeper *tk = &tk_core.timekeeper;
-	unsigned long seq;
-	s64 nsecs_raw, nsecs_real;
-
-	WARN_ON_ONCE(timekeeping_suspended);
-
-	do {
-		seq = read_seqcount_begin(&tk_core.seq);
-
-		*ts_raw = tk->raw_time;
-		ts_real->tv_sec = tk->xtime_sec;
-		ts_real->tv_nsec = 0;
-
-		nsecs_raw  = timekeeping_get_ns(&tk->tkr_raw);
-		nsecs_real = timekeeping_get_ns(&tk->tkr_mono);
-
-	} while (read_seqcount_retry(&tk_core.seq, seq));
-
-	timespec64_add_ns(ts_raw, nsecs_raw);
-	timespec64_add_ns(ts_real, nsecs_real);
-}
-EXPORT_SYMBOL(ktime_get_raw_and_real_ts64);
-
-#endif /* CONFIG_NTP_PPS */
-
 /**
  * adjust_historical_crosststamp - adjust crosstimestamp previous to current interval
  * @total_history_cycles:	Total history length in cycles

@@ -287,11 +287,15 @@ struct correlated_cs {
  * @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 {
 	cycles_t	cycles;
 	ktime_t		real;
 	ktime_t		raw;
+	unsigned int	clock_was_set_seq;
+	u8		cs_was_changed_seq;
 };
 
 #endif /* _LINUX_CLOCKSOURCE_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;
 

@@ -295,13 +295,14 @@ struct sync_device_time_cb {
 	void	 *ctx;
 };
 
+struct system_time_snapshot;
 /*
  * Get cross timestamp between system clock and device clock
  */
 extern int get_device_system_crosststamp(struct sync_device_time_cb *cb,
+					 struct system_time_snapshot *history,
 					 struct system_device_crosststamp *ts);
 
-struct system_time_snapshot;
 /*
  * Simultaneously snapshot realtime and monotonic raw clocks
  */

@@ -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;

@@ -880,6 +881,8 @@ 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;

@@ -932,14 +935,83 @@ EXPORT_SYMBOL(ktime_get_raw_and_real_ts64);
 #endif /* CONFIG_NTP_PPS */
 
 /**
+ * adjust_historical_crosststamp - adjust crosstimestamp previous to current interval
+ * @total_history_cycles:	Total history length in cycles
+ * @partial_history_cycles:	Cycle offset into history (fractional part)
+ * @total_history_monoraw:	Total history length in monotonic raw ns
+ * @total_history_realtime:	Total history length in realtime ns
+ * @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 void adjust_historical_crosststamp(cycle_t total_history_cycles,
+					  cycle_t partial_history_cycles,
+					  ktime_t total_history_monoraw,
+					  ktime_t total_history_realtime,
+					  bool discontinuity,
+					  struct system_device_crosststamp *ts)
+{
+	struct timekeeper *tk = &tk_core.timekeeper;
+	u64 corr_monoraw;
+	u64 corr_realtime;
+
+	/*
+	 * Scale the monotonic raw time delta by:
+	 *	partial_history_cycles / total_history_cycles
+	 */
+	corr_monoraw = (ktime_to_ns(total_history_monoraw) *
+			partial_history_cycles) / total_history_cycles;
+	/*
+	 * 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_realtime = (corr_monoraw * tk->tkr_mono.mult) /
+			tk->tkr_raw.mult;
+	else
+		corr_realtime = (ktime_to_ns(total_history_realtime) *
+				 partial_history_cycles)/total_history_cycles;
+
+	/* Fixup monotonic raw and real time time values */
+	ts->sys_monoraw = ktime_sub_ns(ts->sys_monoraw, corr_monoraw);
+	ts->sys_realtime = ktime_sub_ns(ts->sys_realtime, corr_realtime);
+}
+
+/*
+ * cycle_between - true if test occurs chronologically between before and after
+ */
+static bool cycle_between(cycles_t before, cycles_t test, cycles_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
  *	system counter from the device driver
+ *@history_ref:		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
  */
 int get_device_system_crosststamp(struct sync_device_time_cb *sync_devicetime,
+				  struct system_time_snapshot *history_ref,
 				  struct system_device_crosststamp *xtstamp)
 {
 	struct timekeeper *tk = &tk_core.timekeeper;

@@ -949,6 +1021,12 @@ int get_device_system_crosststamp(struct sync_device_time_cb *sync_devicetime,
 	ktime_t base_real;
 	s64 nsec_raw;
 	s64 nsec_real;
+	cycles_t cycles;
+	cycle_t now;
+	cycle_t interval_start;
+	unsigned int clock_was_set_seq;
+	u8 cs_was_changed_seq;
+	bool do_interp;
 	int ret;
 
 	do {

@@ -970,6 +1048,23 @@ int get_device_system_crosststamp(struct sync_device_time_cb *sync_devicetime,
 		 */
 		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)) {
+			cs_was_changed_seq = tk->cs_was_changed_seq;
+			clock_was_set_seq = tk->clock_was_set_seq;
+			cycles = interval_start;
+			do_interp = true;
+		} else {
+			do_interp = false;
+		}
+
 
 		base_real = ktime_add(tk->tkr_mono.base,
 				      tk_core.timekeeper.offs_real);

@@ -983,6 +1078,41 @@ int get_device_system_crosststamp(struct sync_device_time_cb *sync_devicetime,
 
 	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 total_history_cycles, partial_history_cycles;
+		ktime_t history_monoraw, history_realtime;
+		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_ref ||
+		    !cycle_between(history_ref->cycles,
+				   system_counterval.cycles, interval_start) ||
+		    history_ref->cs_was_changed_seq != cs_was_changed_seq)
+			return -EINVAL;
+		partial_history_cycles = cycles - system_counterval.cycles;
+		history_monoraw = ktime_sub(xtstamp->sys_monoraw,
+					    history_ref->raw);
+		history_realtime = ktime_sub(xtstamp->sys_realtime,
+					     history_ref->real);
+		total_history_cycles = cycles - history_ref->cycles;
+		discontinuity =
+			history_ref->clock_was_set_seq != clock_was_set_seq;
+		adjust_historical_crosststamp(total_history_cycles,
+					      partial_history_cycles,
+					      history_monoraw,
+					      history_realtime, discontinuity,
+					      xtstamp);
+	}
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(get_device_system_crosststamp);

@@ -85,7 +85,7 @@
 #define X86_FEATURE_P4		( 3*32+ 7) /* "" P4 */
 #define X86_FEATURE_CONSTANT_TSC ( 3*32+ 8) /* TSC ticks at a constant rate */
 #define X86_FEATURE_UP		( 3*32+ 9) /* smp kernel running on up */
-/* free, was #define X86_FEATURE_FXSAVE_LEAK ( 3*32+10) * "" FXSAVE leaks FOP/FIP/FOP */
+#define X86_FEATURE_ART		(3*32+10) /* Platform has always running timer (ART) */
 #define X86_FEATURE_ARCH_PERFMON ( 3*32+11) /* Intel Architectural PerfMon */
 #define X86_FEATURE_PEBS	( 3*32+12) /* Precise-Event Based Sampling */
 #define X86_FEATURE_BTS		( 3*32+13) /* Branch Trace Store */

@@ -29,6 +29,8 @@ static inline cycles_t get_cycles(void)
 	return rdtsc();
 }
 
+extern struct correlated_cs art_timestamper;
+
 extern void tsc_init(void);
 extern void mark_tsc_unstable(char *reason);
 extern int unsynchronized_tsc(void);

@@ -949,10 +949,36 @@ static struct notifier_block time_cpufreq_notifier_block = {
 	.notifier_call  = time_cpufreq_notifier
 };
 
+#define ART_CPUID_LEAF (0x15)
+/* The denominator will never be less that 2 */
+#define ART_MIN_DENOMINATOR (2)
+
+static u32 art_to_tsc_numerator;
+static u32 art_to_tsc_denominator;
+
+/*
+ * If ART is present detect the numerator:denominator to convert to TSC
+ */
+static void detect_art(void)
+{
+	unsigned int unused[2];
+
+	if (boot_cpu_data.cpuid_level >= ART_CPUID_LEAF) {
+		cpuid(ART_CPUID_LEAF, &art_to_tsc_denominator,
+		      &art_to_tsc_numerator, unused, unused+1);
+
+		if (art_to_tsc_denominator >= ART_MIN_DENOMINATOR)
+			set_cpu_cap(&boot_cpu_data, X86_FEATURE_ART);
+	}
+}
+
 static int __init cpufreq_tsc(void)
 {
 	if (!cpu_has_tsc)
 		return 0;
+
+	detect_art();
+
 	if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
 		return 0;
 	cpufreq_register_notifier(&time_cpufreq_notifier_block,

@@ -1071,6 +1097,24 @@ int unsynchronized_tsc(void)
 	return 0;
 }
 
+/*
+ * Convert ART to TSC given numerator/denominator found in detect_art()
+ */
+static u64 convert_art_to_tsc(struct correlated_cs *cs, u64 cycles)
+{
+	u64 tmp, res;
+
+	res = (cycles / art_to_tsc_denominator) * art_to_tsc_numerator;
+	tmp = (cycles % art_to_tsc_denominator) * art_to_tsc_numerator;
+	res += tmp / art_to_tsc_denominator;
+
+	return res;
+}
+
+struct correlated_cs art_timestamper = {
+	.convert	= convert_art_to_tsc,
+};
+EXPORT_SYMBOL(art_timestamper);
 
 static void tsc_refine_calibration_work(struct work_struct *work);
 static DECLARE_DELAYED_WORK(tsc_irqwork, tsc_refine_calibration_work);

@@ -1142,6 +1186,8 @@ static void tsc_refine_calibration_work(struct work_struct *work)
 		(unsigned long)tsc_khz % 1000);
 
 out:
+	if (boot_cpu_has(X86_FEATURE_ART))
+		art_timestamper.related_cs = &clocksource_tsc;
 	clocksource_register_khz(&clocksource_tsc, tsc_khz);
 }
 

@@ -267,4 +267,18 @@ struct system_counterval_t {
 	struct clocksource	*cs;
 };
 
+/*
+ * 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;
+	cycle_t			(*convert)(struct correlated_cs *cs,
+					   cycle_t cycles);
+};
+
 #endif /* _LINUX_CLOCKSOURCE_H */

@@ -255,4 +255,16 @@ static inline void clocksource_probe(void) {}
 #define CLOCKSOURCE_ACPI_DECLARE(name, table_id, fn)		\
 	ACPI_DECLARE_PROBE_ENTRY(clksrc, name, table_id, 0, NULL, 0, fn)
 
+/*
+ * struct system_counterval_t - system counter value with the pointer to the
+ *	corresponding clocksource
+ * @cycles:	System counter value
+ * @cs:		Clocksource corresponding to system counter value. Used by
+ *	timekeeping code to verify comparibility of two cycle values
+ */
+struct system_counterval_t {
+	cycle_t			cycles;
+	struct clocksource	*cs;
+};
+
 #endif /* _LINUX_CLOCKSOURCE_H */

@@ -266,6 +266,41 @@ extern void timekeeping_inject_sleeptime64(struct timespec64 *delta);
 extern void ktime_get_raw_and_real_ts64(struct timespec64 *ts_raw,
 				        struct timespec64 *ts_real);
 
+
+/*
+ * struct system_device_crosststamp - system/device cross-timestamp
+ *	(syncronized capture)
+ * @device:		Device time
+ * @sys_realtime:	Realtime simultaneous with device time
+ * @sys_monoraw:	Monotonic raw simultaneous with device time
+ */
+struct system_device_crosststamp {
+	ktime_t device;
+	ktime_t sys_realtime;
+	ktime_t sys_monoraw;
+};
+
+struct system_counterval_t;
+/*
+ * struct get_sync_device_time_cb - Provides method to capture device time
+ *	synchronized with raw system counter value
+ * @get_time:	Callback providing synchronized capture of device time
+ *		and system counter. Returns 0 on success, < 0 on failure
+ * @ctx:	Context provided to callback function
+ */
+struct sync_device_time_cb {
+	int	(*get_time)(ktime_t *device_time,
+			    struct system_counterval_t *system_counterval,
+			    void *ctx);
+	void	 *ctx;
+};
+
+/*
+ * Get cross timestamp between system clock and device clock
+ */
+extern int get_device_system_crosststamp(struct sync_device_time_cb *cb,
+					 struct system_device_crosststamp *ts);
+
 /*
  * Persistent clock related interfaces
  */

@@ -901,6 +901,62 @@ EXPORT_SYMBOL(ktime_get_raw_and_real_ts64);
 #endif /* CONFIG_NTP_PPS */
 
 /**
+ * get_device_system_crosststamp - Synchronously capture system/device timestamp
+ * @sync_devicetime:	Callback to get simultaneous device time and
+ *	system counter from the device driver
+ * @xtstamp:		Receives simultaneously captured system and device time
+ *
+ * Reads a timestamp from a device and correlates it to system time
+ */
+int get_device_system_crosststamp(struct sync_device_time_cb *sync_devicetime,
+				  struct system_device_crosststamp *xtstamp)
+{
+	struct timekeeper *tk = &tk_core.timekeeper;
+	unsigned long seq;
+	struct system_counterval_t system_counterval;
+	ktime_t base_raw;
+	ktime_t base_real;
+	s64 nsec_raw;
+	s64 nsec_real;
+	int ret;
+
+	do {
+		seq = read_seqcount_begin(&tk_core.seq);
+		/*
+		 * Try to synchronously capture device time and a system
+		 * counter value calling back into the device driver
+		 */
+		ret = sync_devicetime->get_time(&xtstamp->device,
+						&system_counterval,
+						sync_devicetime->ctx);
+		if (ret)
+			return ret;
+
+		/*
+		 * Verify that the clocksource associated with the captured
+		 * system counter value is the same as the currently installed
+		 * timekeeper clocksource
+		 */
+		if (tk->tkr_mono.clock != system_counterval.cs)
+			return -ENODEV;
+
+		base_real = ktime_add(tk->tkr_mono.base,
+				      tk_core.timekeeper.offs_real);
+		base_raw = tk->tkr_raw.base;
+
+		nsec_real = timekeeping_cycles_to_ns(&tk->tkr_mono,
+						     system_counterval.cycles);
+		nsec_raw = timekeeping_cycles_to_ns(&tk->tkr_raw,
+						    system_counterval.cycles);
+	} while (read_seqcount_retry(&tk_core.seq, seq));
+
+	xtstamp->sys_realtime = ktime_add_ns(base_real, nsec_real);
+	xtstamp->sys_monoraw = ktime_add_ns(base_raw, nsec_raw);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(get_device_system_crosststamp);
+
+/**
  * do_gettimeofday - Returns the time of day in a timeval
  * @tv:		pointer to the timeval to be set
  *