--- zzzz-none-000/linux-2.6.32.61/Documentation/networking/timestamping.txt	2013-06-10 09:43:48.000000000 +0000
+++ ar10-7272-687/linux-2.6.32.61/Documentation/networking/timestamping.txt	2017-01-26 13:51:06.000000000 +0000
@@ -156,15 +156,19 @@
 in the skb with skb_hwtstamp_set().
 
 Time stamps for outgoing packets are to be generated as follows:
-- In hard_start_xmit(), check if skb_hwtstamp_check_tx_hardware()
-  returns non-zero. If yes, then the driver is expected
-  to do hardware time stamping.
+- In hard_start_xmit(), check if (skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP)
+  is set no-zero. If yes, then the driver is expected to do hardware time
+  stamping.
 - If this is possible for the skb and requested, then declare
-  that the driver is doing the time stamping by calling
-  skb_hwtstamp_tx_in_progress(). A driver not supporting
-  hardware time stamping doesn't do that. A driver must never
-  touch sk_buff::tstamp! It is used to store how time stamping
-  for an outgoing packets is to be done.
+  that the driver is doing the time stamping by setting the flag
+  SKBTX_IN_PROGRESS in skb_shinfo(skb)->tx_flags , e.g. with
+
+      skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;
+
+  You might want to keep a pointer to the associated skb for the next step
+  and not free the skb. A driver not supporting hardware time stamping doesn't
+  do that. A driver must never touch sk_buff::tstamp! It is used to store
+  software generated time stamps by the network subsystem.
 - As soon as the driver has sent the packet and/or obtained a
   hardware time stamp for it, it passes the time stamp back by
   calling skb_hwtstamp_tx() with the original skb, the raw
@@ -175,6 +179,6 @@
   this would occur at a later time in the processing pipeline
   than other software time stamping and therefore could lead
   to unexpected deltas between time stamps.
-- If the driver did not call skb_hwtstamp_tx_in_progress(), then
+- If the driver did not set the SKBTX_IN_PROGRESS flag (see above), then
   dev_hard_start_xmit() checks whether software time stamping
   is wanted as fallback and potentially generates the time stamp.