netdev - Re: [PATCH 2/2] net: dsa: mv88e6xxx: Handle single-chip-address OF property

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Date:   Sun, 24 Apr 2022 00:41:22 +1000
From:   Nathan Rossi <nathan@...hanrossi.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH 2/2] net: dsa: mv88e6xxx: Handle single-chip-address OF property

On Sun, 24 Apr 2022 at 00:07, Andrew Lunn <andrew@...n.ch> wrote:
>
> On Sat, Apr 23, 2022 at 01:14:27PM +0000, Nathan Rossi wrote:
> > Handle the parsing and use of single chip addressing when the switch has
> > the single-chip-address property defined. This allows for specifying the
> > switch as using single chip addressing even when mdio address 0 is used
> > by another device on the bus. This is a feature of some switches (e.g.
> > the MV88E6341/MV88E6141) where the switch shares the bus only responding
> > to the higher 16 addresses.
>
> Hi Nathan
>
> I think i'm missing something in this explanation:
>
> smi.c says:
>
> /* The switch ADDR[4:1] configuration pins define the chip SMI device address
>  * (ADDR[0] is always zero, thus only even SMI addresses can be strapped).
>  *
>  * When ADDR is all zero, the chip uses Single-chip Addressing Mode, assuming it
>  * is the only device connected to the SMI master. In this mode it responds to
>  * all 32 possible SMI addresses, and thus maps directly the internal devices.
>  *
>  * When ADDR is non-zero, the chip uses Multi-chip Addressing Mode, allowing
>  * multiple devices to share the SMI interface. In this mode it responds to only
>  * 2 registers, used to indirectly access the internal SMI devices.
>  *
>  * Some chips use a different scheme: Only the ADDR4 pin is used for
>  * configuration, and the device responds to 16 of the 32 SMI
>  * addresses, allowing two to coexist on the same SMI interface.
>  */
>
> So if ADDR = 0, it takes up the whole bus. And in this case reg = 0.
> If ADDR != 0, it is in multi chip mode, and DT reg = ADDR.
>
> int mv88e6xxx_smi_init(struct mv88e6xxx_chip *chip,
>                        struct mii_bus *bus, int sw_addr)
> {
>         if (chip->info->dual_chip)
>                 chip->smi_ops = &mv88e6xxx_smi_dual_direct_ops;
>         else if (sw_addr == 0)
>                 chip->smi_ops = &mv88e6xxx_smi_direct_ops;
>         else if (chip->info->multi_chip)
>                 chip->smi_ops = &mv88e6xxx_smi_indirect_ops;
>         else
>                 return -EINVAL;
>
> This seems to implement what is above. smi_direct_ops == whole bus,
> smi_indirect_ops == multi-chip mode.
>
> In what situation do you see this not working? What device are you
> using, what does you DT look like, and what at the ADDR value?

The device I am using is the MV88E6141, it follows the second scheme
such that it only responds to the upper 16 of the 32 SMI addresses in
single chip addressing mode. I am able to define the switch at address
0, and everything works. However in the device I am using (Netgate
SG-3100) the ethernet phys for the non switch ethernet interfaces are
also on the same mdio bus as the switch. One of those phys is
configured with address 0. Defining both the ethernet-phy and switch
as address 0 does not work.

The device tree I have looks like:

&mdio {
    status = "okay";
    pinctrl-0 = <&mdio_pins>;
    pinctrl-names = "default";

    phy0: ethernet-phy@0 {
        status = "okay";
        reg = <0>;
    };

    phy1: ethernet-phy@1 {
        status = "okay";
        reg = <1>;
    };

    switch0: switch0@16 {
        compatible = "marvell,mv88e6141", "marvell,mv88e6085";
        single-chip-address;
        reg = <16>; /* first port in single address mode */
        dsa,member = <0 0>;
        status = "okay";

... ports/mdio nodes ...
    };
};

Thanks,
Nathan

>
> Thanks
>         Andrew