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 08:49:32 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Richard Cochran <richardcochran@...il.com>,
        Köry Maincent <kory.maincent@...tlin.com>,
        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, 2 Mar 2023 11:49:26 +0000 Russell King (Oracle) wrote:
> (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.)

Don't wanna waste too much of your time with the questions since
I haven't done much research but - wouldn't MAC timestamp be a better
choice more often (as long as it's a real, to-spec PTP stamp)? 
Are we picking PHY for historical reasons?

Not that flipping the default would address the problem of regressing
some setups..