netdev - Re: [PATCH net-next 3/6] net: dsa: add support for retrieving the interface mode

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Message-ID: <YtqkxklImfR9gW1Z@shell.armlinux.org.uk>
Date:   Fri, 22 Jul 2022 14:23:18 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Marek Behún <kabel@...nel.org>
Cc:     Vladimir Oltean <olteanv@...il.com>, Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Alvin __ipraga <alsi@...g-olufsen.dk>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Daniel Scally <djrscally@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        DENG Qingfang <dqfext@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        George McCollister <george.mccollister@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hauke Mehrtens <hauke@...ke-m.de>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-acpi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Matthias Brugger <matthias.bgg@...il.com>,
        netdev@...r.kernel.org, Paolo Abeni <pabeni@...hat.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Sean Wang <sean.wang@...iatek.com>,
        UNGLinuxDriver@...rochip.com,
        Vivien Didelot <vivien.didelot@...il.com>,
        Woojung Huh <woojung.huh@...rochip.com>
Subject: Re: [PATCH net-next 3/6] net: dsa: add support for retrieving the
 interface mode

On Fri, Jul 22, 2022 at 02:59:36PM +0200, Marek Behún wrote:
>   The 2.5GBASE-X PCS does not support Clause 37 Auto-Negotiation.
>   Hence, the 1000BASE-X PCS is expected to have its Clause 37
>   Auto-Negotiation functionality disabled so that the /C/ ordered set
>   will not be transmitted. If a 2.5GBASE-X PCS receives /C/ ordered
>   set, then undefined behavior may occur.
>   ...

The reason that's probably stated is because there hasn't been any
standardisation of it, different implementations behave differently,
so they can't define a standard behaviour without breaking what's
already out there.

With mvneta, the reality is that the 2.5G speed is implemented by
changing the clock configuration in the COMPHY block (serdes) - which
basically clocks everything 2.5x faster. I seem to remember mvpp2 is
the same deal.

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