path: root/Documentation/networking
diff options
authorWillem de Bruijn <willemb@google.com>2014-07-14 17:55:30 -0400
committerDavid S. Miller <davem@davemloft.net>2014-07-15 16:32:45 -0700
commit26c4fdb0528ae7c4be9fbc8a8210f3b410e6b5aa (patch)
treefdbf59a354779f01dac0732fa033d5d8a721c399 /Documentation/networking
parent11878b40ed5c5bc20d6a115bae156a5b90b0fb3e (diff)
net-timestamp: document deprecated syststamp
The SO_TIMESTAMPING API defines option SOF_TIMESTAMPING_SYS_HW. This feature is deprecated. It should not be implemented by new device drivers. Existing drivers do not implement it, either -- with one exception. Driver developers are encouraged to expose the NIC hw clock as a PTP HW clock source, instead, and synchronize system time to the HW source. The control flag cannot be removed due to being part of the ABI, nor can the structure scm_timestamping that is returned. Due to the one legacy driver, the internal datapath and structure are not removed. This patch only clearly marks the interface as deprecated. Device drivers should always return a syststamp value of zero. Signed-off-by: Willem de Bruijn <willemb@google.com> ---- We can consider adding a WARN_ON_ONCE in__sock_recv_timestamp if non-zero syststamp is encountered Acked-by: Richard Cochran <richardcochran@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'Documentation/networking')
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.

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