linux-kernel - Re: [PATCH net-next v2 00/10] define and enforce phylink bindings

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Message-ID: <5650a2a3-a36f-441e-b4c2-aa7c751b5af5@arinc9.com>
Date:   Sat, 23 Sep 2023 09:28:41 +0300
From:   Arınç ÜNAL <arinc.unal@...nc9.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     "Russell King (Oracle)" <linux@...linux.org.uk>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
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Subject: Re: [PATCH net-next v2 00/10] define and enforce phylink bindings

On 23.09.2023 01:36, Andrew Lunn wrote:
>> I agree. My patch description here failed to explain the actual issue,
>> which is missing hardware descriptions. Here's what I understand. An
>> ethernet-controller is a MAC. For the MAC to work properly with its link
>> partner, at least one of these must be described:
>> - pointer to a PHY to retrieve link information from the PHY
>> - pointer to a PCS to retrieve link information from the PCS
>> - pointer to an SFP to retrieve link information from the SFP
>> - static link information
> 
> You are missing:
> 
> - The MAC has firmware driving the PHY, nothing for linux to do.
> 
> There are properties in ethernet-controller.yaml the MAC driver would
> however like to use such as local-mac-address, max-frame-size,
> nvmem-cell-names etc.

This is interesting. This is clearly a hardware difference of the ethernet
controller.

I believe this fits case 1. There's still an MDIO bus the ethernet
controller uses, there's still a PHY on the MDIO bus which the ethernet
controller uses. The only difference is the firmware of the ethernet
controller controls... What exactly does the firmware control that a Linux
driver would have controlled instead? Just configuring the link settings of
the MAC?

If it's just MAC link settings, I believe it would make sense to add a
property on the ethernet controller dt-bindings to state that the hardware
controls the MAC link settings on its own. This way, we would still
describe the MDIO bus and PHY of the ethernet controller while also
pointing out that the MAC link settings are not up to a driver to control.

Arınç