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

["Russell King (Oracle)" <linux@armlinux.org.uk>]

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.

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