netdev - Re: [PATCH net-next 0/9] mlxsw: Add PTP support for Spectrum-2 and newer ASICs

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Date:   Wed, 27 Jul 2022 07:05:43 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Ido Schimmel <idosch@...dia.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        pabeni@...hat.com, edumazet@...gle.com, petrm@...dia.com,
        amcohen@...dia.com, danieller@...dia.com, mlxsw@...dia.com
Subject: Re: [PATCH net-next 0/9] mlxsw: Add PTP support for Spectrum-2 and
 newer ASICs

On Wed, Jul 27, 2022 at 09:23:19AM +0300, Ido Schimmel wrote:

> Spectrum-2 and newer ASICs essentially implement a transparent clock
> between all the switch ports, including the CPU port. The hardware will
> generate the UTC time stamp for transmitted / received packets at the

The PTP time scale is TAI, not UTC.

> CPU port, but will compensate for forwarding delays in the ASIC by
> adjusting the correction field in the PTP header (for PTP events) at the
> ingress and egress ports.

If the switch adjusts this automatcally, then the time scale in use is
not relevant.

Thanks,
Richard