Message-Id: <20211118032217.244985-2-alexander.komrakov@broadcom.com>
Date:   Wed, 17 Nov 2021 19:22:17 -0800
From:   Alexander Komrakov <alexander.komrakov@...adcom.com>
To:     linux-kernel@...r.kernel.org
Cc:     alexander.komrakov@...adcom.com
Subject: [PATCH 1/1] Calculate the monotonic clock from the timespec clock to generate PPS elapsed real-time event value and stores the result into /sys/class/pps/pps0/assert_elapsed.

From: alexkom <alexander.komrakov@...adcom.com>

Because we have requirements to make sure the delta between standard time, say the GPS Time, and elapsedRealtime < 1 millisecond, regular linux clock timestamp is not enough for our use case.
The pin PPS will generate elapsedRealtime event at 1 sec boundary which is an exact value of the monotonic clock from the kernel PPS driver (/sys/class/pps/pps0/assert_elapsed).

Whenever AP receives this pulse, kernel's pps driver timestamp this elapsedRealtime event and let this time available via sysfs node (/sys/class/pps/pps0/assert_elapsed).

Signed-off-by: alexkom <alexander.komrakov@...adcom.com>
---
 Documentation/ABI/testing/sysfs-pps | 24 ++++++++++++++++++
 drivers/pps/kapi.c                  | 38 ++++++++++++++++++++++++++---
 drivers/pps/sysfs.c                 | 33 +++++++++++++++++++++++++
 include/linux/pps_kernel.h          |  2 ++
 4 files changed, 94 insertions(+), 3 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-pps b/Documentation/ABI/testing/sysfs-pps
index 25028c7bc37d..054617abeebd 100644
--- a/Documentation/ABI/testing/sysfs-pps
+++ b/Documentation/ABI/testing/sysfs-pps
@@ -1,3 +1,27 @@
+What:		/sys/class/pps/pps0/assert_elapsed
+Date:		October 2021
+Contact:	Alexander Komrakov <alexander.komrakov@...adcom.com>
+Description:
+		The /sys/class/pps/ppsX/assert_elapsed file reports the elapsed real-time assert events
+		and the elapsed real-time assert sequence number of the X-th source in the form:
+
+			<secs>.<nsec>#<sequence>
+
+		If the source has no elapsed real-time assert events the content of this file
+		is empty.
+
+What:		/sys/class/pps/ppsX/clear_elapsed
+Date:		October 2021
+Contact:	Alexander Komrakov <alexander.komrakov@...adcom.com>
+Description:
+		The /sys/class/pps/ppsX/clear_elapsed file reports the elapsed real-time clear events
+		and the elapsed real-time clear sequence number of the X-th source in the form:
+
+			<secs>.<nsec>#<sequence>
+
+		If the source has no elapsed real-time clear events the content of this file
+		is empty.
+
 What:		/sys/class/pps/
 Date:		February 2008
 Contact:	Rodolfo Giometti <giometti@...ux.it>
diff --git a/drivers/pps/kapi.c b/drivers/pps/kapi.c
index d9d566f70ed1..149c29e498fc 100644
--- a/drivers/pps/kapi.c
+++ b/drivers/pps/kapi.c
@@ -23,6 +23,26 @@
 /*
  * Local functions
  */
+ #define NANOSEC_PER_SEC 1000000000 /* 10^9 */
+
+/**
+ * clock_gettime - get the monotonic clock in pps_ktime format
+ * @kt:		pointer to the pps_ktime to be set to raw monotonic time
+ *
+ * The function calculates the monotonic clock from the timespec clock
+ * and stores the result in pps_ktime format in the variable pointed to by @kt.
+ *
+ * The function returns the monotonic clock normalized format in nanosec.
+ */
+static __u64 clock_gettime(struct pps_ktime *kt)
+{
+	struct timespec64 ts = { .tv_sec = 0, .tv_nsec = 0 };
+
+	ktime_get_ts64(&ts);
+	kt->sec = ts.tv_sec;
+	kt->nsec = ts.tv_nsec;
+	return (__u64) ts.tv_sec * NANOSEC_PER_SEC + ts.tv_nsec;
+}
 
 static void pps_add_offset(struct pps_ktime *ts, struct pps_ktime *offset)
 {
@@ -162,11 +182,15 @@ void pps_event(struct pps_device *pps, struct pps_event_time *ts, int event,
 	unsigned long flags;
 	int captured = 0;
 	struct pps_ktime ts_real = { .sec = 0, .nsec = 0, .flags = 0 };
+	struct pps_ktime ts_real_elapsed = { .sec = 0, .nsec = 0, .flags = 0 };
 
 	/* check event type */
 	BUG_ON((event & (PPS_CAPTUREASSERT | PPS_CAPTURECLEAR)) == 0);
+	clock_gettime(&ts_real_elapsed);
+	dev_dbg(pps->dev, "PPS event (monotonic) at %lld.%09d\n",
+			(s64)ts_real_elapsed.sec, ts_real_elapsed.nsec);
 
-	dev_dbg(pps->dev, "PPS event at %lld.%09ld\n",
+	dev_dbg(pps->dev, "PPS event (timestamp) at %lld.%09ld\n",
 			(s64)ts->ts_real.tv_sec, ts->ts_real.tv_nsec);
 
 	timespec_to_pps_ktime(&ts_real, ts->ts_real);
@@ -181,11 +205,15 @@ void pps_event(struct pps_device *pps, struct pps_event_time *ts, int event,
 	pps->current_mode = pps->params.mode;
 	if (event & pps->params.mode & PPS_CAPTUREASSERT) {
 		/* We have to add an offset? */
-		if (pps->params.mode & PPS_OFFSETASSERT)
+		if (pps->params.mode & PPS_OFFSETASSERT) {
+			pps_add_offset(&ts_real_elapsed,
+					&pps->params.assert_off_tu);
 			pps_add_offset(&ts_real,
 					&pps->params.assert_off_tu);
+		}
 
 		/* Save the time stamp */
+		pps->assert_elapsed_tu = ts_real_elapsed;
 		pps->assert_tu = ts_real;
 		pps->assert_sequence++;
 		dev_dbg(pps->dev, "capture assert seq #%u\n",
@@ -195,11 +223,15 @@ void pps_event(struct pps_device *pps, struct pps_event_time *ts, int event,
 	}
 	if (event & pps->params.mode & PPS_CAPTURECLEAR) {
 		/* We have to add an offset? */
-		if (pps->params.mode & PPS_OFFSETCLEAR)
+		if (pps->params.mode & PPS_OFFSETCLEAR)	{
+			pps_add_offset(&ts_real_elapsed,
+					&pps->params.clear_off_tu);
 			pps_add_offset(&ts_real,
 					&pps->params.clear_off_tu);
+		}
 
 		/* Save the time stamp */
+		pps->clear_elapsed_tu = ts_real_elapsed;
 		pps->clear_tu = ts_real;
 		pps->clear_sequence++;
 		dev_dbg(pps->dev, "capture clear seq #%u\n",
diff --git a/drivers/pps/sysfs.c b/drivers/pps/sysfs.c
index 134bc33f6ad0..97721cb01695 100644
--- a/drivers/pps/sysfs.c
+++ b/drivers/pps/sysfs.c
@@ -29,6 +29,21 @@ static ssize_t assert_show(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RO(assert);
 
+static ssize_t assert_elapsed_show(struct device *dev,
+			   struct device_attribute *attr, char *buf)
+{
+	struct pps_device *pps = dev_get_drvdata(dev);
+
+	if (!(pps->info.mode & PPS_CAPTUREASSERT))
+		return 0;
+
+	return sprintf(buf, "%lld.%09d#%d\n",
+			(long long) pps->assert_elapsed_tu.sec,
+			pps->assert_elapsed_tu.nsec,
+			pps->assert_sequence);
+}
+static DEVICE_ATTR_RO(assert_elapsed);
+
 static ssize_t clear_show(struct device *dev, struct device_attribute *attr,
 			  char *buf)
 {
@@ -43,6 +58,22 @@ static ssize_t clear_show(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RO(clear);
 
+static ssize_t clear_elapsed_show(struct device *dev,
+			  struct device_attribute *attr,
+			  char *buf)
+{
+	struct pps_device *pps = dev_get_drvdata(dev);
+
+	if (!(pps->info.mode & PPS_CAPTURECLEAR))
+		return 0;
+
+	return sprintf(buf, "%lld.%09d#%d\n",
+			(long long) pps->clear_elapsed_tu.sec,
+			pps->clear_elapsed_tu.nsec,
+			pps->clear_sequence);
+}
+static DEVICE_ATTR_RO(clear_elapsed);
+
 static ssize_t mode_show(struct device *dev, struct device_attribute *attr,
 			 char *buf)
 {
@@ -81,7 +112,9 @@ static DEVICE_ATTR_RO(path);
 
 static struct attribute *pps_attrs[] = {
 	&dev_attr_assert.attr,
+	&dev_attr_assert_elapsed.attr,
 	&dev_attr_clear.attr,
+	&dev_attr_clear_elapsed.attr,
 	&dev_attr_mode.attr,
 	&dev_attr_echo.attr,
 	&dev_attr_name.attr,
diff --git a/include/linux/pps_kernel.h b/include/linux/pps_kernel.h
index 78c8ac4951b5..1fecaaf4c8b9 100644
--- a/include/linux/pps_kernel.h
+++ b/include/linux/pps_kernel.h
@@ -47,6 +47,8 @@ struct pps_device {
 
 	__u32 assert_sequence;			/* PPS assert event seq # */
 	__u32 clear_sequence;			/* PPS clear event seq # */
+	struct pps_ktime assert_elapsed_tu; /* PPS elapsed rt assert seq # */
+	struct pps_ktime clear_elapsed_tu;  /* PPS elapsed rt clear event seq */
 	struct pps_ktime assert_tu;
 	struct pps_ktime clear_tu;
 	int current_mode;			/* PPS mode at event time */
-- 
2.25.1


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