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

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Date:   Tue, 28 Feb 2023 17:44:35 +0100
From:   Michael Walle <michael@...le.cc>
To:     linux@...linux.org.uk
Cc:     andrew@...n.ch, davem@...emloft.net, f.fainelli@...il.com,
        hkallweit1@...il.com, kory.maincent@...tlin.com, kuba@...nel.org,
        maxime.chevallier@...tlin.com, netdev@...r.kernel.org,
        richardcochran@...il.com, thomas.petazzoni@...tlin.com,
        Michael Walle <michael@...le.cc>
Subject: Re: [PATCH RFC net-next] net: phy: add Marvell PHY PTP support [multicast/DSA issues]

>> 4. Letting drivers override PHY at run time.
>
> I think this is the only sensible solution - we know for example that
> mvpp2 will prefer its PTP implementation as it is (a) higher resolution
> and (b) has more flexibility than what can be provided by the Marvell
> PHYs that it is often used with.

Please also consider that there might be one switch with a shared
PHC and multiple PHYs, each with its own PHC. In this case, it is a
property of the board wether PHY timestamping actually works, because
it will need some kind of synchronization between all the PHYs. Whereas
the MAC timestamping just works. Or we dodge that problem now and these
kind of drivers might not use PHY timestamping. But AFAIK microchip is
working on PHY timestamping for their quad PHYs which are used together
with a LAN9668 switch.

-michael