Commit 92d8f766 authored by Ben Hutchings's avatar Ben Hutchings Committed by David S. Miller
Browse files

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: default avatarBen Hutchings <bhutchings@solarflare.com>
Signed-off-by: default avatarShradha Shah <sshah@solarflare.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent ce320f44

drivers/net/ethernet/sfc/ptp.c

+23 −24
Original line number Diff line number Diff line
@@ -766,37 +766,36 @@ efx_ptp_process_times(struct efx_nic *efx, MCDI_DECLARE_STRUCT_PTR(synch_buf), 
		return -EAGAIN;

	}



	/* Convert the NIC time into kernel time. No correction is required-

	 * this time is the output of a firmware process.

	 */

	mc_time = ptp->nic_to_kernel_time(ptp->timeset[last_good].major,

					  ptp->timeset[last_good].minor, 0);



	/* Calculate delay from actual PPS to last_time */

	delta = ktime_to_timespec(mc_time);

	delta.tv_nsec +=

		last_time->ts_real.tv_nsec -

		(ptp->timeset[last_good].host_start & MC_NANOSECOND_MASK);



	/* It is possible that the seconds rolled over between taking

	/* Calculate delay from last good sync (host time) to last_time.

	 * It is possible that the seconds rolled over between taking

	 * the start reading and the last value written by the host.  The

	 * timescales are such that a gap of more than one second is never

	 * expected.

	 * expected.  delta is *not* normalised.

	 */

	start_sec = ptp->timeset[last_good].host_start >> MC_NANOSECOND_BITS;

	last_sec = last_time->ts_real.tv_sec & MC_SECOND_MASK;

	if (start_sec != last_sec) {

		if (((start_sec + 1) & MC_SECOND_MASK) != last_sec) {

	if (start_sec != last_sec &&

	    ((start_sec + 1) & MC_SECOND_MASK) != last_sec) {

		netif_warn(efx, hw, efx->net_dev,

			   "PTP bad synchronisation seconds\n");

		return -EAGAIN;

		} else {

			delta.tv_sec = 1;

		}

	} else {

		delta.tv_sec = 0;

	}

	delta.tv_sec = (last_sec - start_sec) & 1;

	delta.tv_nsec =

		last_time->ts_real.tv_nsec -

		(ptp->timeset[last_good].host_start & MC_NANOSECOND_MASK);



	/* Convert the NIC time at last good sync into kernel time.

	 * No correction is required - this time is the output of a

	 * firmware process.

	 */

	mc_time = ptp->nic_to_kernel_time(ptp->timeset[last_good].major,

					  ptp->timeset[last_good].minor, 0);



	/* Calculate delay from NIC top of second to last_time */

	delta.tv_nsec += ktime_to_timespec(mc_time).tv_nsec;



	/* Set PPS timestamp to match NIC top of second */

	ptp->host_time_pps = *last_time;

	pps_sub_ts(&ptp->host_time_pps, delta);

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