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

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Date:   Sun, 24 Sep 2023 10:49:49 +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 24/09/2023 06:15, Andrew Lunn wrote:
>>> There is a MAC driver currently under review which does not have a PHY
>>> at all. The MAC is directly connected to a switch, all within one
>>> IC. The link is always running at 5Gbps, the link is always up. It is
>>> physically impossible to connect a PHY, so get_link_settings just
>>> returns hard coded values.
>>
>> The fixed-link property would be used to describe the link of the MAC here.
> 
> Fixed-link make sense for a general purpose MAC which could be
> connected to a PHY, or could also be used without a PHY. fixed-link
> simplifies the code in that the MAC driver does not see a difference,
> it all looks like a PHY.
> 
> However for a MAC which cannot be connected to a PHY, there is no need
> to emulate a PHY. The MAC driver will be simpler. So i would not
> recommend a fixed-link in this situation.

There's a link, it must be described. The MAC driver can configure the link
without reading the fixed-link property as there's no room for guessing.

The phy-handle, pcs-handle, and sfp properties point out there's a PHY. The
fixed-link property can be used standalone to describe MAC to MAC links.

For this specific ethernet controller, the phy-handle, pcs-handle, and sfp
properties can be disallowed on its schema to point out the ethernet
controller cannot be connected to a PHY.

Arınç