net: mdiobus: Set FWNODE_FLAG_NEEDS_CHILD_BOUND_ON_ADD for mdiobus parents

There are many instances of PHYs that depend on a switch to supply a
resource (Eg: interrupts). Switches also expects the PHYs to be probed
by their specific drivers as soon as they are added. If that doesn't
happen, then the switch would force the use of generic PHY drivers for
the PHY even if the PHY might have specific driver available.

fw_devlink=on by design can cause delayed probes of PHY. To avoid, this
we need to set the FWNODE_FLAG_NEEDS_CHILD_BOUND_ON_ADD for the switch's
fwnode before the PHYs are added. The most generic way to do this is to
set this flag for the parent of MDIO busses which is typically the
switch.

For more context:
https://lore.kernel.org/lkml/[email protected]/#t

Fixes: ea718c6 ("Revert "Revert "driver core: Set fw_devlink=on by default""")
Suggested-by: Andrew Lunn <[email protected]>
Signed-off-by: Saravana Kannan <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Saravana Kannan

drivers/net/phy/mdio_bus.c

@@ -525,6 +525,10 @@ int __mdiobus_register(struct mii_bus *bus, struct module *owner)
 	    NULL == bus->read || NULL == bus->write)
 		return -EINVAL;
 
+	if (bus->parent && bus->parent->of_node)
+		bus->parent->of_node->fwnode.flags |=
+					FWNODE_FLAG_NEEDS_CHILD_BOUND_ON_ADD;
+
 	BUG_ON(bus->state != MDIOBUS_ALLOCATED &&
 	       bus->state != MDIOBUS_UNREGISTERED);