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

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Date:   Wed, 1 Mar 2023 20:36:37 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     Köry Maincent <kory.maincent@...tlin.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "Russell King (Oracle)" <linux@...linux.org.uk>, 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 Wed, Mar 01, 2023 at 05:04:08PM +0100, Köry Maincent wrote:
> I suppose the idea of Russell to rate each PTP clocks may be the best one, as
> all others solutions have drawbacks. Does using the PTP clock period value (in
> picoseconds) is enough to decide which PTP is the best one? It is hardware
> specific therefore it is legitimate to be set by the MAC and PHY drivers.

It is not that simple.  In fact, I've never seen an objective
comparision of different HW.  The vendors surely have no reason to
conduct such a study.  Also, the data sheets never make any claim
about synchronization quality.

Thanks,
Richard