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

From: Ido Schimmel <[email-masked]>
Date: Thu, 28 Jul 2022 10:03:17 +0300

On Wed, Jul 27, 2022 at 08:09:47PM -0700, Richard Cochran wrote:
> On Wed, Jul 27, 2022 at 05:44:49PM +0300, Ido Schimmel wrote:
> 
> > Right. The hardware can support a TC operation, but I did not find any
> > Linux interfaces to configure it (did I miss something?) nor got any
> > requirements to support it at the moment.
> 
> linuxptp can operate as a TC, but it sounds like your HW does E2E TC
> without any software support.

Yes. I believe linuxptp only implements a two-step transparent clock,
whereas the hardware supports a one-step transparent clock. Like I said,
I'm not aware of any requirements for that at the moment, but I imagine
we would need a per-netdev interface to instruct the kernel/hardware to
adjust the correction field at ingress/egress for specific message
types.

> 
> P2P TC does need SW support, because the ports must generate peer
> delay requests.

Right. The hardware has the ability to add/reduce a number of
nanoseconds (that it gets from software) from the computed latency on a
per-port and ingress/egress basis. 

> Thanks,
> Richard