netdev - Re: DSA setup IMX6ULL and Marvell 88E6390 with 2 Ethernet Phys

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Date:   Wed, 22 May 2019 18:32:55 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Benjamin Beckmeyer <beb@...-engel.de>
Cc:     netdev@...r.kernel.org
Subject: Re: DSA setup IMX6ULL and Marvell 88E6390 with 2 Ethernet Phys - CPU
 Port is not working

On Wed, May 22, 2019 at 10:33:29AM +0200, Benjamin Beckmeyer wrote:
> Hi all,
> 
> I'm currently working on a custom board with the imx6ull processor and the 6390 
> switching chip. This is our hardware setup. 
> 
> ------------     ---------         ---------    MAC     ------------
> |   i.MX   | MAC |  PHY  |   PHY   |  PHY  |------------|  88E6390 |
> |   6ULL   |-----|KSZ8081|---------|LAN8742|	MDIO	|P0        |
> |          |     |ID 0x1 |         | ID0x0 |------------|          |
> |          |     ---------         ---------            |          |
> |          |	     |                                  |MULTI CHIP|
> |          |	     |MDIO                              |ADDR MODE |
> |          |	     |                                  |          |
> |          |--------------------------------------------|   PHY ID |
> |          |                    MDIO                    |     0x2  |
> ------------						------------

Hi Benjamin

KSZ8081 is a 10/100 PHY, i think.
LAN8742 is also a 10/100 PHY.

However, DSA will configure the CPU port MAC to its maximum speed. So
port 0 will be doing 1G. I don't know if specifying phy-mode = "rmii"
is enough. You should take a look at the port status and configuration
registers, see if the MAC is being forced to 1G, or 100M.

You could add a fixed-phy to port 0 with speed 100. That will at least
get the MAC part configured correctly.

Is the LAN8742 strapped so that on power on it will auto-neg? I've
seen a few board with this back-to-back PHY setup, and they just rely
on the PHYs doing the right thing on power up, no software involved.

   Andrew