netdev - Re: [PATCH v4 2/5] dt-bindings: net: dsa: qca,ar9331 switch documentation

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Date:   Tue, 29 Oct 2019 08:34:19 +0100
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Mark Rutland <mark.rutland@....com>, devicetree@...r.kernel.org,
        Jay Cliburn <jcliburn@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Chris Snook <chris.snook@...il.com>,
        linux-kernel@...r.kernel.org, Ralf Baechle <ralf@...ux-mips.org>,
        "David S. Miller" <davem@...emloft.net>,
        Paul Burton <paul.burton@...s.com>,
        Rob Herring <robh+dt@...nel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        James Hogan <jhogan@...nel.org>,
        Russell King <linux@...linux.org.uk>, netdev@...r.kernel.org,
        linux-mips@...r.kernel.org,
        Vivien Didelot <vivien.didelot@...il.com>
Subject: Re: [PATCH v4 2/5] dt-bindings: net: dsa: qca,ar9331 switch
 documentation

On Wed, Oct 23, 2019 at 02:35:43AM +0200, Andrew Lunn wrote:
> On Tue, Oct 22, 2019 at 07:57:40AM +0200, Oleksij Rempel wrote:
> > Atheros AR9331 has built-in 5 port switch. The switch can be configured
> > to use all 5 or 4 ports. One of built-in PHYs can be used by first built-in
> > ethernet controller or to be used directly by the switch over second ethernet
> > controller.
> > 
> > Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> 
> Hi Oleksij
> 
> What we never really discussed is how this MUXing of the PHY works.
> 
> What i'm worried about is that when we do understand how it works, we
> cannot properly support it using this binding.

good point. i would prefer to make it properly.

> Please could you try to find information about this.

Documentation says:
The PHY interfaces (PHY0, PHY1, PHY2, PHY3 and PHY4) can connect to the switch
in bridge mode. In this case GE0 must be under reset. All five LAN ports are
switched together and connect to the CPU through the GMII interface (MAC0),
which is controlled by the ETH_CFG register bit SW_ONLY_MODE. If GE0 connects
separately to PHY, then MAC5 should be under reset.

There is no SW_ONLY_MODE bit in the documentation.
I found:
CFG_SW_PHY_SWAP - Used to switch the wires connection of PHY port 0 with that of
port 4 in the Ethernet switch. MAC1 and PHY4 are paired while MAC5 and PHY0 are
paired.

CFG_SW_PHY_ADDR_SWAP - Exchanges the address of PHY port 0 with that of
PHY port 4 in the Ethernet switch.

It feels like this are the right bits. I'll try to test it after ELC-E
conference (If you are here, please ping me).
If this are the right bits, should it be registered as separate driver? This
register is on MMIO and not part of the switches MDIO.

Regards,
Oleksij
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