linux-kernel - Re: [PATCH ethtool v1] netlink: add master/slave configuration support

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Message-ID: <20200527102620.legyuohgu2xj7pfk@pengutronix.de>
Date:   Wed, 27 May 2020 12:26:20 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Michal Kubecek <mkubecek@...e.cz>
Cc:     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>,
        "John W. Linville" <linville@...driver.com>,
        David Jander <david@...tonic.nl>, kernel@...gutronix.de,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        Russell King <linux@...linux.org.uk>, mkl@...gutronix.de,
        Marek Vasut <marex@...x.de>,
        Christian Herber <christian.herber@....com>,
        Amit Cohen <amitc@...lanox.com>,
        Petr Machata <petrm@...lanox.com>
Subject: Re: [PATCH ethtool v1] netlink: add master/slave configuration
 support

On Tue, May 26, 2020 at 02:41:39PM +0200, Michal Kubecek wrote:
> On Tue, May 26, 2020 at 11:10:25AM +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>
> > ---
> 
> Please document the new command line argument in both "ethtool --help"
> output and manual page.
> 
> I would also prefer updating the UAPI header copies in a separate commit
> which would update all of them to a state of a specific kernel commit
> (either 4.8-rc1 or current net-next); cherry picking specific changes
> may lead to missing some parts. An easy way would be
> 
>   # switch to kernel repository and check out what you want to copy from
>   make ... INSTALL_HDR_PATH=$somewhere headers_install
>   # switch back to ethtool repository
>   cd uapi
>   find . -type f -exec cp -v ${somewhere}/include/{} {} \;
> 
> Also, as the kernel counterpart is only in net-next at the moment, this
> should probably wait until after ethtool 5.7 release (perhaps it would
> be helpful to have a "next" branch like iproute2). I'll submit my queued
> patches for 5.7 later this week; should have done so long ago but
> I hoped to have the netlink friendly test framework finished before I do
> (test-features.c is tied to ioctl interface too tightly).

OK, should I resend fixed patch now, or wait until kernel 5.8-rc1? 

Regards,
Oleksij
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