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

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Message-ID: <20200415141427.GD25745@shell.armlinux.org.uk>
Date:   Wed, 15 Apr 2020 15:14:27 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Oleksij Rempel <o.rempel@...gutronix.de>
Cc:     Michal Kubecek <mkubecek@...e.cz>, netdev@...r.kernel.org,
        Andrew Lunn <andrew@...n.ch>,
        "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>,
        David Jander <david@...tonic.nl>, kernel@...gutronix.de,
        linux-kernel@...r.kernel.org, mkl@...gutronix.de,
        Marek Vasut <marex@...x.de>
Subject: Re: [PATCH v1] ethtool: provide UAPI for PHY master/slave
 configuration.

On Wed, Apr 15, 2020 at 03:00:34PM +0200, Oleksij Rempel wrote:
> On Wed, Apr 15, 2020 at 02:43:43PM +0200, Michal Kubecek wrote:
> > On Wed, Apr 15, 2020 at 02:19:40PM +0200, Oleksij Rempel wrote:
> > > Cc: Marek Vasut <marex@...x.de>
> > > 
> > > On Wed, Apr 15, 2020 at 02:12:09PM +0200, Oleksij Rempel wrote:
> > > > This UAPI is needed for BroadR-Reach 100BASE-T1 devices. Due to lack of
> > > > auto-negotiation support, we needed to be able to configure the
> > > > MASTER-SLAVE role of the port manually or from an application in user
> > > > space.
> > > > 
> > > > The same UAPI can be used for 1000BASE-T or MultiGBASE-T devices to
> > > > force MASTER or SLAVE role. See IEEE 802.3-2018:
> > > > 22.2.4.3.7 MASTER-SLAVE control register (Register 9)
> > > > 22.2.4.3.8 MASTER-SLAVE status register (Register 10)
> > > > 40.5.2 MASTER-SLAVE configuration resolution
> > > > 45.2.1.185.1 MASTER-SLAVE config value (1.2100.14)
> > > > 45.2.7.10 MultiGBASE-T AN control 1 register (Register 7.32)
> > > > 
> > > > The MASTER-SLAVE role affects the clock configuration:
> > > > 
> > > > -------------------------------------------------------------------------------
> > > > When the  PHY is configured as MASTER, the PMA Transmit function shall
> > > > source TX_TCLK from a local clock source. When configured as SLAVE, the
> > > > PMA Transmit function shall source TX_TCLK from the clock recovered from
> > > > data stream provided by MASTER.
> > > > 
> > > > iMX6Q                     KSZ9031                XXX
> > > > ------\                /-----------\        /------------\
> > > >       |                |           |        |            |
> > > >  MAC  |<----RGMII----->| PHY Slave |<------>| PHY Master |
> > > >       |<--- 125 MHz ---+-<------/  |        | \          |
> > > > ------/                \-----------/        \------------/
> > > >                                                ^
> > > >                                                 \-TX_TCLK
> > > > 
> > > > -------------------------------------------------------------------------------
> > > > 
> > > > Since some clock or link related issues are only reproducible in a
> > > > specific MASTER-SLAVE-role, MAC and PHY configuration, it is beneficial
> > > > to provide generic (not 100BASE-T1 specific) interface to the user space
> > > > for configuration flexibility and trouble shooting.
> > > > 
> > > > Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> > > > ---
> > [...]
> > > > +/* Port mode */
> > > > +#define PORT_MODE_MASTER	0x00
> > > > +#define PORT_MODE_SLAVE		0x01
> > > > +#define PORT_MODE_MASTER_FORCE	0x02
> > > > +#define PORT_MODE_SLAVE_FORCE	0x03
> > > > +#define PORT_MODE_UNKNOWN	0xff
> > 
> > Shouldn't 0 rather be something like PORT_MODE_UNSUPPORTED or
> > PORT_MODE_NONE? If I see correctly, all drivers not setting the new
> > field (which would be all drivers right now and almost all later) will
> > leave the value at 0 which would be interpreted as PORT_MODE_MASTER.
> 
> Yes, you right. I was thinking about it and decided to follow the duplex
> code pattern. Will fix in the next version.

Wouldn't that make PORT_MODE_UNKNOWN unnecessary?

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