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

From: Andrew Lunn <andrew@lunn.ch>
To: Russell King <rmk+kernel@armlinux.org.uk>
Cc: Richard Cochran <richardcochran@gmail.com>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Heiner Kallweit <hkallweit1@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	netdev@vger.kernel.org
Subject: Re: [PATCH RFC net-next] net: phy: add Marvell PHY PTP support
Date: Wed, 15 Jul 2020 20:38:43 +0200	[thread overview]
Message-ID: <20200715183843.GA1256692@lunn.ch> (raw)
In-Reply-To: <E1jvNlE-0001Y0-47@rmk-PC.armlinux.org.uk>

> 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