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

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Date:   Wed, 15 Jul 2020 20:38:43 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Russell King <rmk+kernel@...linux.org.uk>
Cc:     Richard Cochran <richardcochran@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH RFC net-next] net: phy: add Marvell PHY PTP support

> Getting the Kconfig for this correct has been a struggle - particularly
> the combination where PTP support is modular.  It's rather odd to have
> the Marvell PTP support asked before the Marvell PHY support.  I
> couldn't work out any other reasonable way to ensure that we always
> have a valid configuration, without leading to stupidities such as
> having the PTP and Marvell PTP support modular, but non-functional
> because Marvell PHY is built-in.

Hi Russell

How much object code is this adding? All the other PHYs which support
PTP just make it part of the PHY driver, not a standalone module. That
i guess simplifies the conditions. 

Looking at DSDT, it lists

        case MAD_88E1340S:
        case MAD_88E1340:
        case MAD_88E1340M:
        case MAD_SWG65G : 
	case MAD_88E151x:

as being MAD_PHY_PTP_TAI_CAPABLE;

and

	case MAD_88E1548
        case MAD_88E1680:
        case MAD_88E1680M:

as MAD_PHY_1STEP_PTP_CAPABLE;

So maybe we can wire this up to a few more PHYs to 'lower' the
overhead a bit?

> It seems that the Marvell PHY PTP is very similar to that found in
> their DSA chips, which suggests maybe we should share the code, but
> different access methods would be required.

That makes the Kconfig even more complex :-(

     Andrew