netdev - Re: [PATCH v2 2/2] net: phy: mscc: handle the clkout control on some phy variants

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Message-ID: <20200617214518.GA2870745@bogus>
Date:   Wed, 17 Jun 2020 15:45:18 -0600
From:   Rob Herring <robh@...nel.org>
To:     Heiko Stuebner <heiko@...ech.de>
Cc:     davem@...emloft.net, kuba@...nel.org, andrew@...n.ch,
        f.fainelli@...il.com, hkallweit1@...il.com, linux@...linux.org.uk,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        christoph.muellner@...obroma-systems.com,
        Heiko Stuebner <heiko.stuebner@...obroma-systems.com>
Subject: Re: [PATCH v2 2/2] net: phy: mscc: handle the clkout control on some
 phy variants

On Tue, Jun 09, 2020 at 03:31:40PM +0200, Heiko Stuebner wrote:
> From: Heiko Stuebner <heiko.stuebner@...obroma-systems.com>
> 
> At least VSC8530/8531/8540/8541 contain a clock output that can emit
> a predefined rate of 25, 50 or 125MHz.
> 
> This may then feed back into the network interface as source clock.
> So follow the example the at803x already set and introduce a
> vsc8531,clk-out-frequency property to set that output.
> 
> Signed-off-by: Heiko Stuebner <heiko.stuebner@...obroma-systems.com>
> ---
> Hi Andrew,
> 
> I didn't change the property yet, do you have a suggestion on
> how to name it though? Going by the other examples in the
> ethernet-phy.yamls, something like enet-phy-clock-out-frequency ?

The correct thing to do here is make the phy a clock provider and then 
the client side use 'assigned-clock-rate' to set the rate. That has the 
advantage that it also describes the connection of the clock signal. You 
might not need that for a simple case, but I could imagine needing that 
in a more complex case.

Rob