sfc: Rewrite adjustment of PPS event in a clearer way

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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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Ben Hutchings 2014-02-12 18:58:46 +00:00 • committed by David S. Miller

parent ce320f44d6

commit 92d8f766ec

1 changed files with 23 additions and 24 deletions

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51

drivers/net/ethernet/sfc/ptp.c

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