netdev - Re: [PATCH v3 1/3] dt-bindings: net: Add Realtek MDIO controller

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Message-ID: <0e3cfeb1-e012-4361-86ca-3114217a9c5e@alliedtelesis.co.nz>
Date: Fri, 20 Dec 2024 09:44:54 +1300
From: Chris Packham <chris.packham@...iedtelesis.co.nz>
To: Daniel Golle <daniel@...rotopia.org>
Cc: lee@...nel.org, robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
 andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
 kuba@...nel.org, pabeni@...hat.com, tsbogend@...ha.franken.de,
 hkallweit1@...il.com, linux@...linux.org.uk, markus.stockhausen@....de,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org, linux-mips@...r.kernel.org
Subject: Re: [PATCH v3 1/3] dt-bindings: net: Add Realtek MDIO controller

Hi Daniel,

On 18/12/2024 12:54, Daniel Golle wrote:
> On Wed, Dec 18, 2024 at 11:44:59AM +1300, Chris Packham wrote:
>> [...]
>> +patternProperties:
>> +  '^ethernet-phy(@[a-f0-9]+)?':
>> +    type: object
>> +    $ref: ethernet-phy.yaml#
>> +
>> +    properties:
>> +      reg:
>> +        description:
>> +          The MDIO communication on the RTL9300 is abstracted by the switch. At
>> +          the software level communication uses the switch port to address the
>> +          PHY with the actual MDIO bus and address having been setup via the
>> +          realtek,smi-address property.
>> +
>> +      realtek,smi-address:
>> +        $ref: /schemas/types.yaml#/definitions/uint32-array
>> +        description: SMI interface and address for the connected PHY
>> +        items:
>> +          - description: SMI interface number associated with the port.
>> +          - description: SMI address of the PHY for the port.
> What speaks against describing the actual MDIO busses and addresses (ie.
> the hardware) in Device Tree and setting up the hardware mapping between
> ports and SMI bus and address by parsing the DSA switch port description
> in the MDIO driver?
>
> In that way you would not need the additional vendor-specific property
> and on switches with high port density also avoid having to deal with
> bogus "MDIO addresses" greater than 31.

I kind of expected this discussion.

The main problem is I couldn't figure out how to make that work. 
Ultimately I still need to write the MDIO bus arrangement to hardware 
and map back to a port number when doing MDIO accesses. Whether the 
device-tree uses port number as the reg property and a vendor property 
for the SMI address or does it the other way round I'd still need a 
vendor property. There's also a complication that I've got one MDIO 
controller that looks after more than one MDIO interface at the same 
time. I'll have a bit of a think about it over the holidays and see if I 
can come up with anything cleaner.