Re: [net-next] dsa: slave: support phy devices on external MII bus

[Florian Fainelli <f.fainelli@gmail.com>]

On 10/18/2017 09:21 AM, Andrew Lunn wrote:
> Hi Martin
> 
> Sorry for starting a new thread. I deleted the patchset from my mailbox.
> 
> Florian said:
> 
>> The logic goes like this:
>>
>> - try to connect to the PHY via phy-handle
>> - if we have a PHY we are connecting via phy-handle but we need to
>>   divert MDIO reads/writes connect using its address on the diverted
>>   bus
>> - connect using a fixed PHY
>> - finally try using the DSA slave MII bus which would connect to the switch internal PHYs
> 
> This is not quite correct. Looking at the code:
> 
>         phy_dn = of_parse_phandle(port_dn, "phy-handle", 0);
>  ...
> 
>         if (phy_dn) {
>                 int phy_id = of_mdio_parse_addr(&slave_dev->dev, phy_dn);
> 
>                 /* If this PHY address is part of phys_mii_mask, which means
>                  * that we need to divert reads and writes to/from it, then we
>                  * want to bind this device using the slave MII bus created by
>                  * DSA to make that happen.
>                  */
>                 if (!phy_is_fixed && phy_id >= 0 &&
>                     (ds->phys_mii_mask & (1 << phy_id))) {
>                         ret = dsa_slave_phy_connect(p, slave_dev, phy_id);
>                         if (ret) {
>                                 netdev_err(slave_dev, "failed to connect to phy%d: %d\n", phy_id, ret);
>                                 of_node_put(phy_dn);
>                                 return ret;
>                         }
>                 } else {
>                         p->phy = of_phy_connect(slave_dev, phy_dn,
> 
> The first point really is:
> 
> - try to connect to the PHY via phy-handle, if the phy_id is not
> valid, or if the phy_id does not map to a phy that the switch says
> does not exist.
> 
> In your case, all these points are true, so it uses
> dsa_slave_phy_connect().  But we actually want it to use
> of_phy_connect(), which will use the correct bus.
> 
> For some Marvell chips, you cannot actually go on ds->phys_mii_mask.
> These devices can have in built PHYs and SERDES interfaces which can
> be assigned to ports. These SERDES interfaces could have external PHYs
> connected to them, and be on the external MDIO bus. So
> ds->phys_mii_mask indicates there is a PHY, but the phy-handle points
> to a different phy.
> 
> So i think this code block needs to change. If we have a phy-handle,
> use it.  i.e. what Florian _thinks_ it should be doing. If not, then
> use dsa_slave_phy_connect().

I see what you mean now, the logic above gets defeated because it does
not concern itself with the MDIO controller parent of the PHY node
pointed to by phy-handle. So if like Martin you have two MDIO busses,
but both happen to have MDIO addresses that are valid for both busses,
the logic above gets defeated and we wrongly try to attach to the switch
internal MDIO bus under ds->slave_mii_bus.

The easiest fix would certainly to lookup the parent MDIO bus and do
that only if ds->slave_mii_bus->of_node and the parent of the node
pointed to 'phy-handle' match.

Does that work for you?
-- 
Florian