Re: [PATCH 0/5] Support both Ethernet interfaces on i.MX6UL and i.MX7

[Guenter Roeck]

On 4/18/23 05:10, Peter Maydell wrote:
> On Wed, 15 Mar 2023 at 14:52, Guenter Roeck <linux@roeck-us.net> wrote:
> > The SOC on i.MX6UL and i.MX7 has 2 Ethernet interfaces. The PHY on each may
> > be connected to separate MDIO busses, or both may be connected on the same
> > MDIO bus using different PHY addresses. Commit 461c51ad4275 ("Add a phy-num
> > property to the i.MX FEC emulator") added support for specifying PHY
> > addresses, but it did not provide support for linking the second PHY on
> > a given MDIO bus to the other Ethernet interface.
> >
> > To be able to support two PHY instances on a single MDIO bus, two properties
> > are needed: First, there needs to be a flag indicating if the MDIO bus on
> > a given Ethernet interface is connected. If not, attempts to read from this
> > bus must always return 0xffff. Implement this property as phy-connected.
> > Second, if the MDIO bus on an interface is active, it needs a link to the
> > consumer interface to be able to provide PHY access for it. Implement this
> > property as phy-consumer.
>
> So I was having a look at this to see if it was reasonably easy to
> split out the PHY into its own device object, and I'm a bit confused.
> I know basically 0 about MDIO, but wikipedia says that MDIO buses
> have one master (the ethernet MAC) and potentially multiple PHYs.
> However it looks like this patchset has configurations where
> multiple MACs talk to the same MDIO bus. Am I confused about the
> patchset, about the hardware, or about what MDIO supports?

It is quite similar to I2C, a serial interface with one master/controller
and a number of devices (PHYs) connected to it. There is a nice graphic
example at https://prodigytechno.com/mdio-management-data-input-output/.
Not sure I understand what is confusing about it. Can you explain ?

Thanks,
Guenter