netdev - Re: [PATCH] of: of_mdio: Handle properties for non-phy mdio devices

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Date:   Tue, 16 Feb 2021 09:50:02 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Andrew Lunn <andrew@...n.ch>, Nathan Rossi <nathan@...hanrossi.com>
Cc:     netdev@...r.kernel.org, Nathan Rossi <nathan.rossi@...i.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH] of: of_mdio: Handle properties for non-phy mdio devices



On 2/16/2021 5:06 AM, Andrew Lunn wrote:
> On Mon, Feb 15, 2021 at 07:02:18AM +0000, Nathan Rossi wrote:
>> From: Nathan Rossi <nathan.rossi@...i.com>
>>
>> The documentation for MDIO bindings describes the "broken-turn-around",
>> "reset-assert-us", and "reset-deassert-us" properties such that any MDIO
>> device can define them. Other MDIO devices may require these properties
>> in order to correctly function on the MDIO bus.
>>
>> Enable the parsing and configuration associated with these properties by
>> moving the associated OF parsing to a common function
>> of_mdiobus_child_parse and use it to apply these properties for both
>> PHYs and other MDIO devices.
> 
> Hi Nathan
> 
> What device are you using this with?
> 
> The Marvell Switch driver does its own GPIO reset handling. It has a
> better idea when a hardware reset should be applied than what the
> phylib core has. It will also poll the EEPROM busy bit after a
> reset. How long a pause you need after the reset depends on how full
> the EEPROM is.
> 
> And i've never had problems with broken-turn-around with Marvell
> switches.

The patch does make sense though, Broadcom 53125 switches have a broken
turn around and are mdio_device instances, the broken behavior may not
show up with all MDIO controllers used to interface though. For the
reset, I would agree with you this is better delegated to the switch
driver, given that unlike PHY devices, we have no need to know the
mdio_device ID prior to binding the device and the driver together.

> 
> Given the complexity of an Ethernet switch, it is probably better if
> it handles its own reset.
> 
>      Andrew
> 

-- 
Florian