netdev - Re: [PATCH net-next 1/8] dt-bindings: ethernet-controller: support multiple PHY connection types

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Date:   Thu, 18 Nov 2021 17:27:55 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Marek Behún <kabel@...nel.org>
Cc:     netdev@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org
Subject: Re: [PATCH net-next 1/8] dt-bindings: ethernet-controller: support
 multiple PHY connection types

On Wed, Nov 17, 2021 at 11:50:43PM +0100, Marek Behún wrote:
> Sometimes, an ethernet PHY may communicate with ethernet controller with
> multiple different PHY connection types, and the software should be able
> to choose between them.
> 
> Russell King says:
>   conventionally phy-mode has meant "this is the mode we want to operate
>   the PHY interface in" which was fine when PHYs didn't change their
>   mode depending on the media speed
> This is no longer the case, since we have PHYs that can change PHY mode.
> 
> Existing example is the Marvell 88X3310 PHY, which supports connecting
> the MAC with the PHY with `xaui` and `rxaui`. The MAC may also support
> both modes, but it is possible that a particular board doesn't have
> these modes wired (since they use multiple SerDes lanes).
> 
> Another example is one SerDes lane capable of `1000base-x`, `2500base-x`
> and `sgmii` when connecting Marvell switches with Marvell ethernet
> controller. Currently we mention only one of these modes in device-tree,
> and software assumes the other modes are also supported, since they use
> the same SerDes lanes. But a board may be able to support `1000base-x`
> and not support `2500base-x`, for example due to the higher frequency
> not working correctly on a particular board.
> 
> In order for the kernel to know which modes are supported on the board,
> we need to be able to specify them all in the device-tree.
> 
> Change the type of property `phy-connection-type` of an ethernet
> controller to be an array of the enumerated strings, instead of just one
> string. Require at least one item defined.
> 
> Signed-off-by: Marek Behún <kabel@...nel.org>

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew