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doc: update driver TX algorithm in timestamping.txt

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Since cd4d8fdad1 ("net: kernel panic in dev_hard_start_xmit:
remove faulty software TX time stamping") dev_hard_start_xmit()
will not provide software timestamps. It's a responsibility of
the drivers to call skb_tx_timestamp() at the right time.

Cc: linux-doc@vger.kernel.org
Signed-off-by: Jakub Kicinski <kubakici@wp.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jakub Kicinski 2014-03-16 20:32:48 +01:00 committed by David S. Miller
parent 86a2b9cfcc
commit 59cb89e6b7
1 changed files with 3 additions and 3 deletions
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6
Documentation/networking/timestamping.txt
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@ -202,6 +202,9 @@ Time stamps for outgoing packets are to be generated as follows:
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.
- Driver should call skb_tx_timestamp() as close to passing sk_buff to hardware
as possible. skb_tx_timestamp() provides a software time stamp if requested
and hardware timestamping is not possible (SKBTX_IN_PROGRESS not set).
- 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
@ -212,6 +215,3 @@ Time stamps for outgoing packets are to be generated as follows:
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 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.