Re: [PATCH net-next 06/16] net: pcs: xpcs: Avoid creating dummy XPCS MDIO device

Andrew Lunn
2023-12-05T13:52:42Z

On Tue, Dec 05, 2023 at 02:31:41PM +0300, Serge Semin wrote:
> On Tue, Dec 05, 2023 at 10:49:47AM +0000, Russell King (Oracle) wrote:
> > On Tue, Dec 05, 2023 at 01:35:27PM +0300, Serge Semin wrote:
> > > If the DW XPCS MDIO devices are either left unmasked for being auto-probed
> > > or explicitly registered in the MDIO subsystem by means of the
> > > mdiobus_register_board_info() method there is no point in creating the
> > > dummy MDIO device instance in order to get the DW XPCS handler since the
> > > MDIO core subsystem will create the device during the MDIO bus
> > > registration procedure.
> >
>
> > Please reword this overly long sentence.
>
> Ok.
>
> >
> > If they're left unmasked, what prevents them being created as PHY
> > devices?
>
> Not sure I fully get what you meant. If they are left unmasked the
> MDIO-device descriptor will be created by the MDIO subsystem anyway.
> What the point in creating another one?

Saying what Russell said, in a different way:

/*
* Return true if the child node is for a phy. It must either:
* o Compatible string of "ethernet-phy-idX.X"
* o Compatible string of "ethernet-phy-ieee802.3-c45"
* o Compatible string of "ethernet-phy-ieee802.3-c22"
* o In the white list above (and issue a warning)
* o No compatibility string
*
* A device which is not a phy is expected to have a compatible string
* indicating what sort of device it is.
*/
bool of_mdiobus_child_is_phy(struct device_node *child)

So when walking the bus, if a node is found which fits these criteria,
its assumed to be a PHY.

Anything on the MDIO bus which is not a PHY needs to use a compatible.

Andrew