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Message-ID: <410dfe3c-6f99-4054-88f8-0acbd134cfce@lunn.ch>
Date:   Sat, 23 Sep 2023 17:12:40 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Arınç ÜNAL <arinc.unal@...nc9.com>
Cc:     "Russell King (Oracle)" <linux@...linux.org.uk>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Conor Dooley <conor+dt@...nel.org>,
        George McCollister <george.mccollister@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Woojung Huh <woojung.huh@...rochip.com>,
        UNGLinuxDriver@...rochip.com,
        Linus Walleij <linus.walleij@...aro.org>,
        Alvin Šipraga <alsi@...g-olufsen.dk>,
        Clément Léger <clement.leger@...tlin.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        Steen Hegelund <Steen.Hegelund@...rochip.com>,
        Daniel Machon <daniel.machon@...rochip.com>,
        Radhey Shyam Pandey <radhey.shyam.pandey@....com>,
        Daniel Golle <daniel@...rotopia.org>,
        Landen Chao <Landen.Chao@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <magnus.damm@...il.com>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Marek Vasut <marex@...x.de>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        John Crispin <john@...ozen.org>,
        Madalin Bucur <madalin.bucur@....com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Felix Fietkau <nbd@....name>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Oleksij Rempel <linux@...pel-privat.de>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Jose Abreu <joabreu@...opsys.com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Sekhar Nori <nsekhar@...com>,
        Shyam Pandey <radhey.shyam.pandey@...inx.com>,
        mithat.guner@...ont.com, erkin.bozoglu@...ont.com,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH net-next v2 00/10] define and enforce phylink bindings

On Sat, Sep 23, 2023 at 09:28:41AM +0300, Arınç ÜNAL wrote:
> On 23.09.2023 01:36, Andrew Lunn wrote:
> > > I agree. My patch description here failed to explain the actual issue,
> > > which is missing hardware descriptions. Here's what I understand. An
> > > ethernet-controller is a MAC. For the MAC to work properly with its link
> > > partner, at least one of these must be described:
> > > - pointer to a PHY to retrieve link information from the PHY
> > > - pointer to a PCS to retrieve link information from the PCS
> > > - pointer to an SFP to retrieve link information from the SFP
> > > - static link information
> > 
> > You are missing:
> > 
> > - The MAC has firmware driving the PHY, nothing for linux to do.
> > 
> > There are properties in ethernet-controller.yaml the MAC driver would
> > however like to use such as local-mac-address, max-frame-size,
> > nvmem-cell-names etc.
> 
> This is interesting. This is clearly a hardware difference of the ethernet
> controller.
> 
> I believe this fits case 1. There's still an MDIO bus the ethernet
> controller uses, there's still a PHY on the MDIO bus which the ethernet
> controller uses.

Why must there be an MDIO bus? All the bus provides is a communication
channel to the PHY. There are PHYs which are memory mapped, or use
I2C. SFP are a good example of I2C, which Linux maps to MDIO just to
make things simple, but the hardware is I2C. Why must there be a PHY?
Maybe it is a Base-K link, i.e. a baseboard link to a switch, or a BMC
or something.

> The only difference is the firmware of the ethernet
> controller controls... What exactly does the firmware control that a Linux
> driver would have controlled instead? Just configuring the link settings of
> the MAC?

A MAC driver implements struct ethtool_ops:::get_link_settings and
set_link_settings. For a MAC driver using phylib or phylink they
typically then call into phylib or phylink to do the actual work,
maybe with a bit of pre-processing in the MAC driver.

A MAC driver using firmware would typically make an RPC into the
firmware to implement these calls.

There is a MAC driver currently under review which does not have a PHY
at all. The MAC is directly connected to a switch, all within one
IC. The link is always running at 5Gbps, the link is always up. It is
physically impossible to connect a PHY, so get_link_settings just
returns hard coded values.

	Andrew

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