From 59cb89e6b763443c6360f634288c57668efeecc5 Mon Sep 17 00:00:00 2001 From: Jakub Kicinski Date: Sun, 16 Mar 2014 20:32:48 +0100 Subject: doc: update driver TX algorithm in timestamping.txt Since cd4d8fdad1f1 ("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 Signed-off-by: David S. Miller --- Documentation/networking/timestamping.txt | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'Documentation') diff --git a/Documentation/networking/timestamping.txt b/Documentation/networking/timestamping.txt index 048c92b487f6..bc3554124903 100644 --- a/Documentation/networking/timestamping.txt +++ b/Documentation/networking/timestamping.txt @@ -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. -- cgit v1.2.1