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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.
Date
From: alexkom <alexander.komrakov@broadcom.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@broadcom.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@broadcom.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@broadcom.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@linux.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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