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

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Message-ID: <20200415124343.GZ3141@unicorn.suse.cz>
Date:   Wed, 15 Apr 2020 14:43:43 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     netdev@...r.kernel.org
Cc:     Oleksij Rempel <o.rempel@...gutronix.de>,
        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, Russell King <linux@...linux.org.uk>,
        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 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.

Michal