Merge branch 'dsa-mv88e6xxx-Improve-PTP-access-latency'

Andrew Lunn says:

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net: dsa: mv88e6xxx: Improve PTP access latency

PTP needs to retrieve the hardware timestamps from the switch device
in a low latency manor. However ethtool -S and bridge fdb show can
hold the switch register access mutex for a long time. These patches
changes the reading the statistics and the ATU so that the mutex is
released and taken again between each statistic or ATU entry. The PTP
code can then interleave its access to the hardware, keeping its
latency low.
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Signed-off-by: David S. Miller <davem@davemloft.net>