netdev - RE: [PATCH v3 3/4] Add support for driver cross-timestamp to PTP_SYS

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Date:	Mon, 24 Aug 2015 20:16:51 +0000
From:	"Hall, Christopher S" <christopher.s.hall@...el.com>
To:	'Richard Cochran' <richardcochran@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"john.stultz@...aro.org" <john.stultz@...aro.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
	"peterz@...radead.org" <peterz@...radead.org>
Subject: RE: [PATCH v3 3/4] Add support for driver cross-timestamp to
 PTP_SYS_OFFSET ioctl

> -----Original Message-----
> From: Richard Cochran [mailto:richardcochran@...il.com]
> Sent: Sunday, August 23, 2015 4:26 AM
> To: Thomas Gleixner
> Cc: Hall, Christopher S; Kirsher, Jeffrey T; hpa@...or.com;
> mingo@...hat.com; john.stultz@...aro.org; x86@...nel.org; linux-
> kernel@...r.kernel.org; netdev@...r.kernel.org; intel-wired-
> lan@...ts.osuosl.org; peterz@...radead.org
> Subject: Re: [PATCH v3 3/4] Add support for driver cross-timestamp to
> PTP_SYS_OFFSET ioctl
> 
> On Sun, Aug 23, 2015 at 10:15:00AM +0200, Thomas Gleixner wrote:
> > So why can't you take N samples from the synced hardware? It does not
> > make any sense to me to switch to the imprecise mode if nsamples > 1.
> 
> Ok, then I prefer to leave this "imprecise" method in place and ...
> 
> > You can also provide a new IOCTL PTP_SYS_OFFSET_PRECISE which returns
> > -ENOSYS if hardware timestamping is not available and avoid the whole
> > nsamples dance for the case where we can get precise timestamps.
> 
> have this for the new way.
> 
> By keeping the imprecise method, we will be able to run both methods
> on the new hardware.  That will help to quantify how imprecise the old
> method is.

This means: remove code changes from the PTP_SYS_OFFSET ioctl and call getsynctime64() from a new ioctl PTP_SYS_OFFSET_PRECISE.  Right?

And use the same type (struct ptp_sys_offset) for the new ioctl?  Or should a new simplified struct be used? Such as:

struct precise_ptp_sys_offset {
	struct ptp_clock_time device;
	struct ptp_clock_time system;
};

Does it make sense to keep the "cross-timestamp" capabilities flag as-is?

> 
> Thanks,
> Richard

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