netdev - Re: [PATCH spi for-5.4 0/5] Deterministic SPI latency with NXP DSPI driver

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Date:   Wed, 21 Aug 2019 07:08:15 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Mark Brown <broonie@...nel.org>,
        Hubert Feurstein <h.feurstein@...il.com>, mlichvar@...hat.com,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        linux-spi@...r.kernel.org, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH spi for-5.4 0/5] Deterministic SPI latency with NXP DSPI
 driver

On Tue, Aug 20, 2019 at 09:38:45PM -0700, Richard Cochran wrote:
> Overall, the PTP switch use case is well supported by Linux.  The
> synchronization of the management CPU to the PTP, while nice to have,
> is not required to implement a Transparent Clock.  Your specific
> application might require it, but honestly, if the management CPU
> needs good synchronization, then you really aught to feed a PPS from
> the switch into a gpio (for example) on the CPU.

Another way to achieve this is to have a second MAC interface on the
management CPU connected to a spare port on the switch.  Then time
stamping, PHC, ptp4l, and phc2sys work as expected.

Thanks,
Richard