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 15:50:16 +0100
From:   Köry Maincent <kory.maincent@...tlin.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Richard Cochran <richardcochran@...il.com>, andrew@...n.ch,
        davem@...emloft.net, f.fainelli@...il.com, hkallweit1@...il.com,
        kuba@...nel.org, 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 Tue, 28 Feb 2023 13:36:36 +0000
"Russell King (Oracle)" <linux@...linux.org.uk> wrote:

> > Also your series rise the question of which timestamping should be the
> > default, MAC or PHY, without breaking any past or future compatibilities.
> > There is question of using Kconfig or devicetree but each of them seems to
> > have drawbacks:
> > https://lore.kernel.org/netdev/ad4a8d3efbeaacf241a19bfbca5976f9@walle.cc/ 
> > 
> > Do you or Russell have any new thought about it?  
> 
> The only thought I have is that maybe a MAC driver should be able to
> override the default, then at least we have a way to deal with this
> on a case by case basis. However, that's just pulling an idea out of
> the air.
>
> I think what might be useful as a first step is to go through the
> various networking devices to work out which support PTP today, and
> tabulate the result. There shouldn't be any cases where we have both
> the MAC and PHY having PTP support (for the API reasons I've already
> stated) but if there are, that needs to be highlighted.

The only defconfig on that case present on mainline is socfpga_defconfig
(MICREL_PHY and STMMAC_ETH). In fact PHY timestamping is really not spread.
There is only one defconfig which support PTP on both MAC and PHY, therefore
setting the PTP on MAC by default seems the best choice. It won't change the
default behavior when adding new PHY PTP support. Does adding documentation
about socfpga_defconfig is sufficient or should we need to add something
specific to change the default PTP on this case.

Regards,
Köry