On Mon, Sep 17, 2018 at 08:14:04AM +0000, FUSTE Emmanuel wrote:
> Running the command compiled without PTP_SYS_OFFSET_PRECISE support on a 
> kernel (and perhaps the hardware) with PTP_SYS_OFFSET_PRECISE will 
> return a definitively wrong answer.

Yeah, this isn't ideal.

Saying "unknown" is also a bit weird.  People will wonder, why can't
you tell?

How about this:

/* from linux kernel v4.19-rc4 */
struct compat_caps {
        int max_adj;   /* Maximum frequency adjustment in parts per billon. */
        int n_alarm;   /* Number of programmable alarms. */
        int n_ext_ts;  /* Number of external time stamp channels. */
        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. */
        /* Whether the clock supports precise system-device cross timestamps */
        int cross_timestamping;
        int rsv[13];   /* Reserved for future use. */
};

and then

static int do_caps(clockid_t clkid, int cmdc, char *cmdv[])
{
        union {
                struct ptp_clock_caps caps;
                struct compat_caps compat;
        } u;
        ...
        // check u.compat.cross_timestamping
}

Hm?

Thanks,
Richard


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