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

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Date:	Thu, 21 Jul 2016 00:50:33 +0000
From:	"Brown, Aaron F" <aaron.f.brown@...el.com>
To:	Kshitiz Gupta <kshitiz.gupta@...com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	Nathan Sullivan <nathan.sullivan@...com>
CC:	"intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH] igb: fix adjusting ptp timestamps for tx/rx latency

> From: netdev-owner@...r.kernel.org [mailto:netdev-
> owner@...r.kernel.org] On Behalf Of Kshitiz Gupta
> Sent: Saturday, July 16, 2016 12:24 AM
> To: Kirsher, Jeffrey T <jeffrey.t.kirsher@...el.com>; Nathan Sullivan
> <nathan.sullivan@...com>; Brown, Aaron F <aaron.f.brown@...el.com>
> Cc: intel-wired-lan@...ts.osuosl.org; netdev@...r.kernel.org; Kshitiz Gupta
> <kshitiz.gupta@...com>
> 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 <kshitiz.gupta@...com>
> 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 <aaron.f.brown@...el.com>