The phc_ctl program includes an implementation for comparing the PHC
with CLOCK_REALTIME when PTP_SYS_OFFSET ioctls are not supported.
This implementation produces inverted results when compared with the
implementation of the ioctl.
The PTP_SYS_OFFSET ioctls calculate the difference as "CLOCK_REALTIME -
PHC_TIME" while this function calculates "PHC_TIME - CLOCK_REALTIME".
This could produce confusing results if phc_ctl is used on a kernel
which lacks the PTP_SYS_OFFSET ioctls.
Fix this by replacing the bespoke implementation in test_phc with the
clockadj_compare function. That function mimics the interface of
sysoff_measure and correctly computes the time offset between the two
clocks in the same manner as the ioctls do. In addition, it supports
performing multiple samples to reduce inaccuracy.
With this change, the fallback implementation of measurement will match
the behavior of the ioctl based PTP_SYS_OFFSET flows.
Signed-off-by: Jacob Keller <jacob.e.kel...@intel.com>
---
phc_ctl.c | 54 ++++++++++++++++--------------------------------------
1 file changed, 16 insertions(+), 38 deletions(-)
diff --git a/phc_ctl.c b/phc_ctl.c
index 673cb37e3583..e975dd803578 100644
--- a/phc_ctl.c
+++ b/phc_ctl.c
@@ -90,26 +90,6 @@ static int install_handler(int signum, void(*handler)(int))
return 0;
}
-static int64_t calculate_offset(struct timespec *ts1,
- struct timespec *rt,
- struct timespec *ts2)
-{
- int64_t interval;
- int64_t offset;
-
-#define NSEC_PER_SEC 1000000000ULL
- /* calculate interval between clock realtime */
- interval = (ts2->tv_sec - ts1->tv_sec) * NSEC_PER_SEC;
- interval += ts2->tv_nsec - ts1->tv_nsec;
-
- /* assume PHC read occured half way between CLOCK_REALTIME reads */
-
- offset = (rt->tv_sec - ts1->tv_sec) * NSEC_PER_SEC;
- offset += (rt->tv_nsec - ts1->tv_nsec) - (interval / 2);
-
- return offset;
-}
-
static void usage(const char *progname)
{
fprintf(stderr,
@@ -335,34 +315,32 @@ static int do_caps(clockid_t clkid, int cmdc, char
*cmdv[])
static int do_cmp(clockid_t clkid, int cmdc, char *cmdv[])
{
- struct timespec ts, rta, rtb;
- int64_t sys_offset, delay = 0, offset;
+ int64_t sys_offset, delay;
uint64_t sys_ts;
- int method;
+ int method, fd;
- method = sysoff_probe(CLOCKID_TO_FD(clkid), 9);
+#define N_SAMPLES 9
- if (method >= 0 && sysoff_measure(CLOCKID_TO_FD(clkid), method, 9,
+ fd = CLOCKID_TO_FD(clkid);
+
+ method = sysoff_probe(fd, N_SAMPLES);
+
+ if (method >= 0 && sysoff_measure(fd, method, N_SAMPLES,
&sys_offset, &sys_ts, &delay) >= 0) {
- pr_notice( "offset from CLOCK_REALTIME is %"PRId64"ns\n",
- sys_offset);
+ pr_notice("offset from CLOCK_REALTIME is %"PRId64"ns\n",
+ sys_offset);
return 0;
}
- memset(&ts, 0, sizeof(ts));
- memset(&rta, 0, sizeof(rta));
- memset(&rtb, 0, sizeof(rtb));
- if (clock_gettime(CLOCK_REALTIME, &rta) ||
- clock_gettime(clkid, &ts) ||
- clock_gettime(CLOCK_REALTIME, &rtb)) {
- pr_err("cmp: failed clock reads: %s\n",
- strerror(errno));
+ if (clockadj_compare(clkid, CLOCK_REALTIME, N_SAMPLES,
+ &sys_offset, &sys_ts, &delay)) {
+ pr_err("cmp: failed to compare clocks: %s\n",
+ strerror(errno));
return -1;
}
- offset = calculate_offset(&rta, &ts, &rtb);
- pr_notice( "offset from CLOCK_REALTIME is approximately %"PRId64"ns\n",
- offset);
+ pr_notice("offset from CLOCK_REALTIME is approximately %"PRId64"ns\n",
+ sys_offset);
return 0;
}
--
2.31.1.331.gb0c09ab8796f
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