From 92d8f766ecce190dc2aa5d1aa9a5f5381e831641 Mon Sep 17 00:00:00 2001 From: Ben Hutchings Date: Wed, 12 Feb 2014 18:58:46 +0000 Subject: [PATCH] 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 Signed-off-by: Shradha Shah Signed-off-by: David S. Miller --- drivers/net/ethernet/sfc/ptp.c | 51 +++++++++++++++++----------------- 1 file changed, 25 insertions(+), 26 deletions(-) diff --git a/drivers/net/ethernet/sfc/ptp.c b/drivers/net/ethernet/sfc/ptp.c index 7d0de5002f41..28275e395cb8 100644 --- a/drivers/net/ethernet/sfc/ptp.c +++ b/drivers/net/ethernet/sfc/ptp.c @@ -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. + /* 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. 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 && + ((start_sec + 1) & MC_SECOND_MASK) != last_sec) { + netif_warn(efx, hw, efx->net_dev, + "PTP bad synchronisation seconds\n"); + return -EAGAIN; + } + 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 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 - * 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. - */ - 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) { - netif_warn(efx, hw, efx->net_dev, - "PTP bad synchronisation seconds\n"); - return -EAGAIN; - } else { - delta.tv_sec = 1; - } - } else { - delta.tv_sec = 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);