sfc: Rewrite adjustment of PPS event in a clearer way
There is substantial latency in generation and handling of PPS events from the NIC, which we have to correct for before passing a host timestamp to the PPS subsystem. We compare clocks with the MC, giving us two offsets to subtract from the timestamp generated by pps_get_ts(): (a) Time from the last good sync (where we got host and NIC timestamps for nearly the same instant) to the time we called pps_get_ts() (b) Time from NIC top of second to the last good sync We currently calculate (a) + (b) in a quite confusing way. Instead, calculate (a) completely, then add (b) to it. Signed-off-by: Ben Hutchings <bhutchings@solarflare.com> Signed-off-by: Shradha Shah <sshah@solarflare.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -766,37 +766,36 @@ efx_ptp_process_times(struct efx_nic *efx, MCDI_DECLARE_STRUCT_PTR(synch_buf),
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return -EAGAIN;
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}
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/* Convert the NIC time into kernel time. No correction is required-
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* this time is the output of a firmware process.
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/* Calculate delay from last good sync (host time) to last_time.
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* It is possible that the seconds rolled over between taking
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* the start reading and the last value written by the host. The
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* timescales are such that a gap of more than one second is never
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* expected. delta is *not* normalised.
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*/
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start_sec = ptp->timeset[last_good].host_start >> MC_NANOSECOND_BITS;
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last_sec = last_time->ts_real.tv_sec & MC_SECOND_MASK;
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if (start_sec != last_sec &&
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((start_sec + 1) & MC_SECOND_MASK) != last_sec) {
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netif_warn(efx, hw, efx->net_dev,
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"PTP bad synchronisation seconds\n");
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return -EAGAIN;
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}
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delta.tv_sec = (last_sec - start_sec) & 1;
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delta.tv_nsec =
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last_time->ts_real.tv_nsec -
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(ptp->timeset[last_good].host_start & MC_NANOSECOND_MASK);
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/* Convert the NIC time at last good sync into kernel time.
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* No correction is required - this time is the output of a
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* firmware process.
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*/
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mc_time = ptp->nic_to_kernel_time(ptp->timeset[last_good].major,
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ptp->timeset[last_good].minor, 0);
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/* Calculate delay from actual PPS to last_time */
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delta = ktime_to_timespec(mc_time);
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delta.tv_nsec +=
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last_time->ts_real.tv_nsec -
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(ptp->timeset[last_good].host_start & MC_NANOSECOND_MASK);
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/* It is possible that the seconds rolled over between taking
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* the start reading and the last value written by the host. The
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* timescales are such that a gap of more than one second is never
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* expected.
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*/
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start_sec = ptp->timeset[last_good].host_start >> MC_NANOSECOND_BITS;
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last_sec = last_time->ts_real.tv_sec & MC_SECOND_MASK;
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if (start_sec != last_sec) {
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if (((start_sec + 1) & MC_SECOND_MASK) != last_sec) {
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netif_warn(efx, hw, efx->net_dev,
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"PTP bad synchronisation seconds\n");
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return -EAGAIN;
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} else {
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delta.tv_sec = 1;
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}
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} else {
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delta.tv_sec = 0;
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}
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/* Calculate delay from NIC top of second to last_time */
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delta.tv_nsec += ktime_to_timespec(mc_time).tv_nsec;
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/* Set PPS timestamp to match NIC top of second */
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ptp->host_time_pps = *last_time;
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pps_sub_ts(&ptp->host_time_pps, delta);
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