Re: [Linuxptp-users] Jump of ~UTC-TAI offset after taking the interface down and up

[Richard C. <ric...@gm...>]

On Mon, Aug 20, 2018 at 01:28:25PM +0000, FUSTE Emmanuel wrote:
> I think the big jump is because the PHC was stopped and completely reset 
> between a down/up sequence.

Right.  The driver resets the time to the system time value (which is UTC).

> Is it an expected behavior ?

For ptp4l?  Yes.

For the ifdown/ifup of the driver?  I would call it a driver bug.  It
is completely illogical that that bringing the interface down and up
again would change the stored time.

I have complained about this on netdev before, but to no avail.  There
drivers that do all of their bringup/teardown in their .open/close
callbacks and *not* in the .probe/remove methods.  It may be that
the HW forces implementation in some cases.

But in at least one case, where *I* wrote a perfectly adequate PHC
driver that sets the clock exactly once, in probe/remove, the $corp
developers when ahead and moved that into open/close.  Brilliant.

> Could we do something on the ptp4l side to 
> address this case ?

Yes, you can use the 'step_threshold' option.

Thanks,
Richard