RE: [PATCH] igb: fix adjusting ptp timestamps for tx/rx latency

From: netdev-owner@vger.kernel.org [mailto:netdev-
owner@vger.kernel.org] On Behalf Of Kshitiz Gupta
Sent: Saturday, July 16, 2016 12:24 AM
To: Kirsher, Jeffrey T <redacted>; Nathan Sullivan
[off-list ref]; Brown, Aaron F [off-list ref]
Cc: intel-wired-lan@lists.osuosl.org; netdev@vger.kernel.org; Kshitiz Gupta
[off-list ref]
Subject: [PATCH] igb: fix adjusting ptp timestamps for tx/rx latency

Fix PHY delay compensation math in igb_ptp_tx_hwtstamp() and
igb_ptp_rx_rgtstamp. Add PHY delay compensation in
igb_ptp_rx_pktstamp().

In the IGB driver, there are two functions that retrieve timestamps
received by the PHY - igb_ptp_rx_rgtstamp() and igb_ptp_rx_pktstamp().
The previous commit only changed igb_ptp_rx_rgtstamp(), and the change
was incorrect.

There are two instances in which PHY delay compensations should be
made:

- Before the packet transmission over the PHY, the latency between
  when the packet is timestamped and transmission of the packets,
  should be an add operation, but it is currently a subtract.

- After the packets are received from the PHY, the latency between
  the receiving and timestamping of the packets should be a subtract
  operation, but it is currently an add.

Signed-off-by: Kshitiz Gupta <redacted>
Fixes: 3f544d2 (igb: adjust ptp timestamps for tx/rx latency)
---
 drivers/net/ethernet/intel/igb/igb_ptp.c | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

I think I was so engrossed in checking the values for 10 / 100 / 1000 delays that I completely missed the reversed add / subtract when looking at 3f544d2.  Thanks for catching that.
Tested-by: Aaron Brown <redacted>