[PATCH v6 0/8] ptp: IEEE 1588 hardware clock support

[Christoph Lameter]

On Thu, 23 Sep 2010, john stultz wrote:

> This was my initial gut reaction as well, but in the end, I agree with
> Richard that in the case of one or multiple PTP hardware clocks, we
> really can't abstract over the different time domains.

My (arguably still superficial) review of the source does not show
anything that would make me reach that conclusion.

> I really don't think the PTP clock can be used as a clocksource sanely.
>
> First, the hardware access is much to slow for system timekeeping.

The HPET or pit timesource are also quite slow these days. You only need
access periodically to essentially tune the TSC ratio.

> Second, there is the problem that the system time is a software clock,
> and adjustments made (like freq) are made in the layer that interprets
> the underlying hardware cycle counter. Adjustments made in PTP (in order
> to sync the network timestamps) are made at the hardware level.