netdev - RE: [net-next 07/12] ixgbe: Enable timesync clock-out feature for PPS support on X540

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Date:	Fri, 11 May 2012 18:10:17 +0000
From:	"Keller, Jacob E" <jacob.e.keller@...el.com>
To:	Richard Cochran <richardcochran@...il.com>
CC:	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"gospo@...hat.com" <gospo@...hat.com>,
	"sassmann@...hat.com" <sassmann@...hat.com>
Subject: RE: [net-next 07/12] ixgbe: Enable timesync clock-out feature for
 PPS support on X540

> -----Original Message-----
> From: Richard Cochran [mailto:richardcochran@...il.com]
> Sent: Thursday, May 10, 2012 10:41 PM
> To: Keller, Jacob E
> Cc: Kirsher, Jeffrey T; davem@...emloft.net; netdev@...r.kernel.org;
> gospo@...hat.com; sassmann@...hat.com
> Subject: Re: [net-next 07/12] ixgbe: Enable timesync clock-out feature for PPS
> support on X540
> 
> On Thu, May 10, 2012 at 10:08:44PM +0000, Keller, Jacob E wrote:
> >
> > Oops stupid mail program sent that on accident. Anyways: I think you
> > might be right, Richard. We don't read those timestamp values unless
> > the stat err bit for timestamps is set on the descriptor. But I am not
> > sure what happens when the tjmestamped packet is dropped off the end
> > of the ring. What would you propose here? How can we detect if this
> > timestamp doesn't match the packet? I can look into using the extra
> > hardware features for matching timestamps. That might be a more useful, in
> that it would help prevent this case.
> 
> [ Talking about the Rx time stamping locking from other patch... ]
> 
> The IGB provides some PTP event packet identification fields (seqNum,
> etc) just for the purpose of matching time stamps to packets. Some of the
> other PHC drivers (ixp4xx, dp83640) have code that does the matching.
> 

Ixgbe has the sequence number also. I'll take a look at the PHC drivers
that match already, and see how difficult it would be to perform this check.

- Jake

> HTH,
> Richard
> 

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