Re: [PATCH v4 1/4] Produce system time from correlated clocksource

Thomas Gleixner
2015-10-13T19:16:47Z

On Tue, 13 Oct 2015, Richard Cochran wrote:

> On Tue, Oct 13, 2015 at 09:51:02AM +0200, Thomas Gleixner wrote:
> >
> > You are restricting the problem space to this particular use
> > case. There are other use cases where PTP is not available or not the
> > relevant reference, but you still want to correlate time domains to
> > ART.
>
> They may well be other use cases, but they have not been identified
> here. The PTP to media clock problem has a very simple solution. You
> do not need a history of system time stamps to solve it.

Well, these use cases are not in the focus of Christopher, but I have
a few in my head. Think industrial fieldbusses.

> Even if you wanted to correlate the system time's UTC with the media
> clock, still you don't need any shadow history for that. Just feed
> (ART, UTC) pairs into the DSP at a regular rate, and let the DSP do
> the math. This does not need to be part of the central time keeping
> code at all.

That's not working. The firmware is not going to change, no matter
what.

Thanks,

tglx