netdev - Re: [PATCH v4 net-next 3/8] net: phy: bcm84881: move the in-band capability check where it belongs

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Message-ID: <Y30MNsLs164iX3x5@shell.armlinux.org.uk>
Date:   Tue, 22 Nov 2022 17:51:50 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        UNGLinuxDriver@...rochip.com,
        bcm-kernel-feedback-list@...adcom.com,
        Madalin Bucur <madalin.bucur@....nxp.com>,
        Camelia Groza <camelia.groza@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Maxim Kochetkov <fido_max@...ox.ru>,
        Sean Anderson <sean.anderson@...o.com>,
        Antoine Tenart <atenart@...nel.org>,
        Michael Walle <michael@...le.cc>,
        Raag Jadav <raagjadav@...il.com>,
        Siddharth Vadapalli <s-vadapalli@...com>,
        Ong Boon Leong <boon.leong.ong@...el.com>,
        Colin Foster <colin.foster@...advantage.com>,
        Marek Behun <marek.behun@....cz>
Subject: Re: [PATCH v4 net-next 3/8] net: phy: bcm84881: move the in-band
 capability check where it belongs

On Tue, Nov 22, 2022 at 02:24:51PM +0200, Vladimir Oltean wrote:
> On Tue, Nov 22, 2022 at 09:38:43AM +0000, Russell King (Oracle) wrote:
> > 88E1111 is the commonly used accessible PHY on gigabit SFPs, as this
> > PHY implements I2C access natively.
> 
> As a side question, I suppose it would be possible to put PHYs on copper
> SFP modules even if they don't natively implement I2C access. In that case,
> if configuration from the host is at all available, how does that happen,
> is there some sort of protocol translator (I2C -> MDIO) on the module?

Modules that provide access to the PHY seem to do so on I2C address 0x56
and require specific I2C access patterns. I think the 88e1111 set a kind
of "standard" and many follow that or similar.

Some just don't give any kind of access to the PHY - for example, the
Mikrotik modules have an AR803x PHY on them, but there is no way to
access it.

> Do you know of any part number for an I2C controlled MDIO controller?

I think many that don't use a microcontroller - for example, when
someone puts an 88x3310, bcm84881, the protocols are very similar but
timing may vary.

Some of the patches from Marek provided a different way - via the 0x50
or 0x51 "eeprom" addresses, accessing specific addresses with in those
spaces, and if I remember correctly, requiring a "password" to enable
access.

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