netdev - Re: [PATCH RFC russell-king 3/4] net: phy: marvell10g: change MACTYPE according to phydev->interface

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Message-ID: <20200812162232.GT1551@shell.armlinux.org.uk>
Date:   Wed, 12 Aug 2020 17:22:32 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Marek Behún <marek.behun@....cz>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Baruch Siach <baruch@...s.co.il>,
        Chris Healy <cphealy@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH RFC russell-king 3/4] net: phy: marvell10g: change
 MACTYPE according to phydev->interface

On Wed, Aug 12, 2020 at 06:13:33PM +0200, Marek Behún wrote:
> The MACTYPE is not being lost. But changing it requires Port Software
> Reset, which resets the link, so it cannot be done for example in
> read_status.

Wouldn't the right place to configure it be in the config_init()
method - which is called once we have a MAC attaching to the PHY?
As I mentioned, if we had a way to pass the MAC interface supported
mask into phylib, config_init() could then use that to determine what
to do.

> I think the MACTYPE should be set sometime during PHY initialisation,
> and only once: either to XFI with rate matching, if the underlying MAC
> does not support lower modes, or to 10gbase-r/2500base-x/sgmii mode, if
> the underlying MAC supports only slower modes than 10G.

Yes - only changing the MAC type if we have good reason to do so to
support other rates.

There is a related problem however.  Note that if you have an 88x3310
(non-P) in the SFP, then when rate matching is enabled, the PHY will
_not_ generate pause frames, and the PHY expects the MAC to be
configured to pace itself to the slower speed.  I don't believe we
have support in MACs for that, but phylib and therefore phylink
provides the information:

	interface - 10GBASE-R
	speed - media speed
	pause - media pause modes

So, if speed != SPEED_10000 and there are no pause modes, we should,
for the sake of the entire link, pace the MAC to the media speed by
controlling its egress rate.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!