On 04/11/2017 04:14 PM, Andrew Lunn wrote: >> To give some more background and rational for this change. >> >> On a platform where we have a parent MDIO bus, backed by the >> mdio-bcm-unimac.c driver, we also register a slave MII bus (through >> net/dsa/dsa2.c) which is parented to this UniMAC MDIO bus through an >> assignment of of_node. This slave MII bus is created in order to >> intercept reads/writes to problematic addresses (e.g: that clashes with >> another piece of hardware). >> >> This means that the slave DSA MII bus inherits all child nodes from the >> originating master MII bus. This also means that when the slave MII bus >> is probed via of_mdiobus_register(), we probe the same devices twice: >> once through the master, another time through the slave. > > Ah, O.K. This makes more sense. On the hardware i have, we get three > deep in MDIO busses. We have the FEC mdio bus. On top of that we have > a gpio-mux-mdio, and on top of that we have the mv88e6xxx mdio > bus. And i've never seen issues. > > So your real problem here is you have two mdio busses using the same > device tree properties. I would actually say that is just plain > broken. >From a Device Tree/HW representation perspective, we do have the external BCM53125 switch physically attached to the 7445/7278 SWITCH_MDIO bus (backed by mdio-bcm-unimac) so in that regard the representation is correct. There is also an integrated Gigabit PHY (bcm7xxx) which is attached to that bus. >From a SW perspective though, we want to talk to the integrated Gigabit PHY using mdio-bcm-unimac but talk to the external BCM53125 switch using the slave MII bus created by the bcm_sf2 driver in order to create an isolation. We need to inherit some of the parent (mdio-bcm-unimac) child DT nodes (such as the BCM53125), but not the GPHY. The easiest solution I found was to use this patch. Using mdiobus_register() instead of of_mdiobus_register() was considered, but then, the child BCM53125 has no more "visbility" into the OF world at all, and it matters, because this switch is also driven via a DSA switch driver and its Ethernet data-path is connected to one port of the bcm_sf2 switch.. Thankfully the HW bug was fixed eventually ;) -- Florian -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
