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

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Date:   Sat, 23 Apr 2022 16:07:25 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Nathan Rossi <nathan@...hanrossi.com>
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 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?

Thanks
	Andrew