path: root/Documentation/networking/timestamping.txt
diff options
authorWillem de Bruijn <willemb@google.com>2014-07-25 18:01:32 -0400
committerDavid S. Miller <davem@davemloft.net>2014-07-29 11:39:50 -0700
commit4d276eb6a478307a28ae843836c455bf04b37a3c (patch)
tree2915bc3a3e8ea825e7b02349b05915aaff8a91eb /Documentation/networking/timestamping.txt
parent68a360e82e55c9b35097e7be7f7991d8f401032f (diff)
net: remove deprecated syststamp timestamp
The SO_TIMESTAMPING API defines three types of timestamps: software, hardware in raw format (hwtstamp) and hardware converted to system format (syststamp). The last has been deprecated in favor of combining hwtstamp with a PTP clock driver. There are no active users in the kernel. The option was device driver dependent. If set, but without hardware support, the correct behavior is to return zero in the relevant field in the SCM_TIMESTAMPING ancillary message. Without device drivers implementing the option, this field is effectively always zero. Remove the internal plumbing to dissuage new drivers from implementing the feature. Keep the SOF_TIMESTAMPING_SYS_HARDWARE flag, however, to avoid breaking existing applications that request the timestamp. Signed-off-by: Willem de Bruijn <willemb@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'Documentation/networking/timestamping.txt')
1 files changed, 2 insertions, 10 deletions
diff --git a/Documentation/networking/timestamping.txt b/Documentation/networking/timestamping.txt
index 8b4ad809df27..897f942b976b 100644
--- a/Documentation/networking/timestamping.txt
+++ b/Documentation/networking/timestamping.txt
@@ -88,15 +88,8 @@ hwtimeraw is the original hardware time stamp. Filled in if
SOF_TIMESTAMPING_RAW_HARDWARE is set. No assumptions about its
relation to system time should be made.
-hwtimetrans is the hardware time stamp transformed so that it
-corresponds as good as possible to system time. This correlation is
-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. This
-field is DEPRECATED. Only one driver computes this value. New device
-drivers must leave this zero. Instead, they can expose the hardware
+hwtimetrans is always zero. This field is deprecated. It used to hold
+hw timestamps converted to system time. Instead, 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,
@@ -191,7 +184,6 @@ struct skb_shared_hwtstamps {
* since arbitrary point in time
ktime_t hwtstamp;
- ktime_t syststamp; /* hwtstamp transformed to system time base */
Time stamps for outgoing packets are to be generated as follows:

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