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Date:   Tue, 5 May 2020 21:44:52 +0200
From:   Michal Kubecek <mkubecek@suse.cz>
To:     netdev@vger.kernel.org
Cc:     Oleksij Rempel <o.rempel@pengutronix.de>,
        Andrew Lunn <andrew@lunn.ch>,
        "David S. Miller" <davem@davemloft.net>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Heiner Kallweit <hkallweit1@gmail.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        David Jander <david@protonic.nl>, kernel@pengutronix.de,
        linux-kernel@vger.kernel.org, Russell King <linux@armlinux.org.uk>,
        mkl@pengutronix.de, Marek Vasut <marex@denx.de>,
        Christian Herber <christian.herber@nxp.com>
Subject: Re: [PATCH net-next v6 1/2] ethtool: provide UAPI for PHY
 master/slave configuration.
Message-ID: <20200505194452.GP8237@lion.mk-sys.cz>
References: <20200505063506.3848-1-o.rempel@pengutronix.de>
 <20200505063506.3848-2-o.rempel@pengutronix.de>
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On Tue, May 05, 2020 at 08:35:05AM +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@pengutronix.de>
> ---

I'm OK with the ethtool part and interface between ethtool and phy code
but I'm not confident to review the low level genphy stuff so it would
be nice if someone could check that.

Michal