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-rw-r--r--Documentation/networking/timestamping.txt10
1 files changed, 8 insertions, 2 deletions
diff --git a/Documentation/networking/timestamping.txt b/Documentation/networking/timestamping.txt
index bc3554124903..8b4ad809df27 100644
--- a/Documentation/networking/timestamping.txt
+++ b/Documentation/networking/timestamping.txt
@@ -40,7 +40,7 @@ the set bits correspond to data that is available, then the control
message will not be generated:
SOF_TIMESTAMPING_SOFTWARE: report systime if available
-SOF_TIMESTAMPING_SYS_HARDWARE: report hwtimetrans if available
+SOF_TIMESTAMPING_SYS_HARDWARE: report hwtimetrans if available (deprecated)
SOF_TIMESTAMPING_RAW_HARDWARE: report hwtimeraw if available
It is worth noting that timestamps may be collected for reasons other
@@ -94,7 +94,13 @@ not perfect; as a consequence, sorting packets received via different
NICs by their hwtimetrans may differ from the order in which they were
received. hwtimetrans may be non-monotonic even for the same NIC.
Filled in if SOF_TIMESTAMPING_SYS_HARDWARE is set. Requires support
-by the network device and will be empty without that support.
+by the network device and will be empty without that support. This
+field is DEPRECATED. Only one driver computes this value. New device
+drivers must leave this zero. Instead, they can expose the hardware
+clock device on the NIC directly as a HW PTP clock source, to allow
+time conversion in userspace and optionally synchronize system time
+with a userspace PTP stack such as linuxptp. For the PTP clock API,
+see Documentation/ptp/ptp.txt.
SIOCSHWTSTAMP, SIOCGHWTSTAMP: