netdev - Re: [PATCH net-next v2 2/3] net: ethernet: fec: Allow configuration of MDIO bus speed

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Message-ID: <3cb32a99-c684-03fd-c471-1d061ca97d4b@gmail.com>
Date:   Fri, 17 Apr 2020 17:34:56 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Andrew Lunn <andrew@...n.ch>, David Miller <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Heiner Kallweit <hkallweit1@...il.com>, fugang.duan@....com,
        Chris Healy <Chris.Healy@....aero>
Subject: Re: [PATCH net-next v2 2/3] net: ethernet: fec: Allow configuration
 of MDIO bus speed

Hi Andrew,

On 4/17/2020 5:03 PM, Andrew Lunn wrote:
> MDIO busses typically operate at 2.5MHz. However many devices can
> operate at faster speeds. This then allows more MDIO transactions per
> second, useful for Ethernet switch statistics, or Ethernet PHY TDR
> data. Allow the bus speed to be configured, using the standard
> "clock-frequency" property, which i2c busses use to indicate the bus
> speed.
> 
> Suggested-by: Chris Healy <Chris.Healy@....aero>
> Signed-off-by: Andrew Lunn <andrew@...n.ch>

This does look good to me, however if we go down that road, it looks 
like we should also support a 'mdio-max-frequency' per MDIO child node 
in order to scale up and down the frequency accordingly, and do that on 
a per transfer basis. So this means that we would likely need to add a 
callback into the mii_bus structure to configure the MDIO bus controller 
clock rate based on the min between what the controller and the device 
supports.

It seems to me that everything works in your case because you have a 
single MDIO device which is a switch, right?
-- 
Florian