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

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Date:   Thu, 2 Mar 2023 13:19:38 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Köry Maincent <kory.maincent@...tlin.com>,
        Jakub Kicinski <kuba@...nel.org>, andrew@...n.ch,
        davem@...emloft.net, f.fainelli@...il.com, hkallweit1@...il.com,
        netdev@...r.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>
Subject: Re: [PATCH RFC net-next] net: phy: add Marvell PHY PTP support
 [multicast/DSA issues]

On Thu, Mar 02, 2023 at 11:49:26AM +0000, Russell King (Oracle) wrote:

> Therefore, I believe that the Marvell PHY PTP implementation is all
> round inferior to that found in the Marvell PP2 MAC, and hence why I
> believe that the PP2 MAC implementation should be used by default over
> the PHY.

Yeah, that phy sure sounds like a lemon.

> (In essence, because of all the noise when trying the Marvell PHY with
> ptp4l, I came to the conlusion that NTP was a far better solution to
> time synchronisation between machines than PTP would ever be due to
> the nose induced by MDIO access. However, I should also state that I
> basically gave up with PTP in the end because hardware support is
> overall poor, and NTP just works - and I'd still have to run NTP for
> the machines that have no PTP capabilities. PTP probably only makes
> sense if one has a nice expensive grand master PTP clock on ones
> network, and all the machines one wants to synchronise have decent
> PTP implementations.)

Yes, NTP is really what most people need, and with PTP you really must
carefully select the hardware.  There is lots of PTP junk on the
market.

Thanks,
Richard