[Linuxptp-users] master offset is increased in some condition

[Takahiro S. <tsh...@gm...>]

Hello,

I faced the issue that the master offset is increased in some condition.

The log is like below:
ptp4l[4597]: master offset -337052518 s2 adj -50000000 path delay    9249190
ptp4l[4597]: master offset -369835430 s2 adj -50000000 path delay    9249190
ptp4l[4597]: master offset -402770356 s2 adj -50000000 path delay    9402100
ptp4l[4597]: master offset -435105809 s2 adj -50000000 path delay    8954993
ptp4l[4597]: master offset -468838529 s2 adj -50000000 path delay    9904481
ptp4l[4597]: master offset -501932158 s2 adj -50000000 path delay   10212862
ptp4l[4597]: master offset -534480670 s2 adj -50000000 path delay    9979646
ptp4l[4597]: master offset -567281355 s2 adj -50000000 path delay    9997963
ptp4l[4597]: master offset -600064139 s2 adj -50000000 path delay    9997963
ptp4l[4597]: master offset -633393240 s2 adj -50000000 path delay   10544184
ptp4l[4597]: master offset -666177880 s2 adj -50000000 path delay   10544184
ptp4l[4597]: master offset -698614796 s2 adj -50000000 path delay   10198444
ptp4l[4597]: master offset -730351808 s2 adj -50000000 path delay    9152352
ptp4l[4597]: master offset -763135840 s2 adj -50000000 path delay    9152352

This issue is happened in the latest linuxptp too.

This issue is happened when adj is -50000000 or 50000000.
If the adj is -50000000 with s2(SERVO_LOCKED), clock_ppb is called with
-adj.

enum servo_state clock_synchronize(struct clock *c,
:
:
case SERVO_LOCKED:
clock_ppb(c->clkid, -adj);
:


static void clock_ppb(clockid_t clkid, double ppb)
{
struct timex tx;
memset(&tx, 0, sizeof(tx));
tx.modes = ADJ_FREQUENCY;
tx.freq = (long) (ppb * 65.536);
if (clock_adjtime(clkid, &tx) < 0)
pr_err("failed to adjust the clock: %m");
}
If ppb is 50000000, then the result is 50000000 * 65.536 = 3276800000.
tx.freq = (long)3276800000 = -1018167296.
I think the tx.freq is overflowed. This is unexpected result.

I think tx.freq should be under 0x7fffffff.
If so, the max adh should be 0x7fffffff/65.536 = 32767999.9847...

If I chage the EG20T ptp driver, the result seems OK.

static struct ptp_clock_info ptp_pch_caps = {
.owner = THIS_MODULE,
.name = "PCH timer",
// .max_adj = 50000000,
.max_adj = 32767999, // Changed the max_adj by TS.

(Question)
1. Is my modification correct ?
2. Is it better to correct it in another part?

Thanks and Best regards,
Takahiro Shimizu