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

[Hall, Christopher S]

> -----Original Message-----
> From: Richard Cochran [mailto:richardcochran@xxxxxxxxx]
> Sent: Sunday, August 23, 2015 4:26 AM
> To: Thomas Gleixner
> Cc: Hall, Christopher S; Kirsher, Jeffrey T; hpa@xxxxxxxxx;
> mingo@xxxxxxxxxx; john.stultz@xxxxxxxxxx; x86@xxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; intel-wired-
> lan@xxxxxxxxxxxxxxxx; peterz@xxxxxxxxxxxxx
> 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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