netdev - Re: [PATCH v1] ethtool: provide UAPI for PHY master/slave configuration.

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Message-ID: <20200417143548.GS25745@shell.armlinux.org.uk>
Date:   Fri, 17 Apr 2020 15:35:48 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Oleksij Rempel <o.rempel@...gutronix.de>,
        "David S. Miller" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Michal Kubecek <mkubecek@...e.cz>,
        David Jander <david@...tonic.nl>, kernel@...gutronix.de,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        mkl@...gutronix.de
Subject: Re: [PATCH v1] ethtool: provide UAPI for PHY master/slave
 configuration.

On Fri, Apr 17, 2020 at 04:32:39PM +0200, Andrew Lunn wrote:
> On Fri, Apr 17, 2020 at 11:11:45AM +0100, Russell King - ARM Linux admin wrote:
> > On Wed, Apr 15, 2020 at 11:57:39PM +0200, Andrew Lunn wrote:
> > > > diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> > > > index c8b0c34030d32..d5edf2bc40e43 100644
> > > > --- a/drivers/net/phy/phy_device.c
> > > > +++ b/drivers/net/phy/phy_device.c
> > > > @@ -604,6 +604,7 @@ struct phy_device *phy_device_create(struct mii_bus *bus, int addr, u32 phy_id,
> > > >  	dev->asym_pause = 0;
> > > >  	dev->link = 0;
> > > >  	dev->interface = PHY_INTERFACE_MODE_GMII;
> > > > +	dev->master_slave = PORT_MODE_UNKNOWN;
> > > 
> > > phydev->master_slave is how we want the PHY to be configured. I don't
> > > think PORT_MODE_UNKNOWN makes any sense in that contest. 802.3 gives
> > > some defaults. 9.12 should be 0, meaning manual master/slave
> > > configuration is disabled. The majority of linux devices are end
> > > systems. So we should default to a single point device. So i would
> > > initialise PORT_MODE_SLAVE, or whatever we end up calling that.
> > 
> > I'm not sure that is a good idea given that we use phylib to drive
> > the built-in PHYs in DSA switches, which ought to prefer master mode
> > via the "is a multiport device" bit.
> 
> O.K. So i assume you mean we should read from the PHY at probe time
> what it is doing, in order to initialise dev->master_slave?
> 
> I would be happy with that.

Yes, I think it's a good idea to preserve the current operating mode
of the PHY as that's essentially what we're doing today by not
currently touching the bit.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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