netdev - Re: [PATCH RFC net-next] net: phy: add Marvell PHY PTP support

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Message-ID: <ZAEWs041NRZkc4Xx@hoboy.vegasvil.org>
Date:   Thu, 2 Mar 2023 13:35:47 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     Köry Maincent <kory.maincent@...tlin.com>
Cc:     linux@...linux.org.uk, andrew@...n.ch, davem@...emloft.net,
        f.fainelli@...il.com, hkallweit1@...il.com, kuba@...nel.org,
        netdev@...r.kernel.org,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH RFC net-next] net: phy: add Marvell PHY PTP support

On Thu, Mar 02, 2023 at 11:37:52AM +0100, Köry Maincent wrote:

> On my side with a zynqMP SOM (cadence MACB MAC) the synchronization of the PHY
> PTP clock is way better: +/-50ppb. Do you have an idea about the difference? 
> Which link partner were you using? stm32mp157 hardware PTP on my side.

The predecessor Zynq 7000 SoC had a PTP MAC that was unusable.  So
much so, that the vendor simply deleted the PTP chapters from the data
sheet without a word.  IIRC, the newer MP has a different implementation,
but maybe they also flubbed that one?

In any case, this is another example of how a good PHY implementation
covers for a poor MAC one.

Thanks,
Richard