netdev - Re: [PATCH] of: of_mdio: count number of regitered phys

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Date:   Wed, 1 Jul 2020 08:47:58 +0000
From:   <Claudiu.Beznea@...rochip.com>
To:     <f.fainelli@...il.com>, <andrew@...n.ch>
CC:     <hkallweit1@...il.com>, <linux@...linux.org.uk>,
        <robh+dt@...nel.org>, <frowand.list@...il.com>,
        <netdev@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] of: of_mdio: count number of regitered phys

Hi Andrew, Florian,

On 30.06.2020 06:35, Florian Fainelli wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On 6/29/2020 5:45 PM, Andrew Lunn wrote:
>> On Mon, Jun 29, 2020 at 10:26:36AM +0300, Claudiu Beznea wrote:
>>> In case of_mdiobus_register_phy()/of_mdiobus_register_device()
>>> returns -ENODEV for all PHYs in device tree or for all scanned
>>> PHYs there is a chance that of_mdiobus_register() to
>>> return success code although no PHY devices were registered.
>>> Add a counter that increments every time a PHY was registered
>>> to avoid the above scenario.
>>
>> Hi Claudiu
>>
>> There is a danger here this will break something. Without this patch,
>> an empty bus is O.K. But with this patch, a bus without a PHY is a
>> problem.
>>
>> Take for example FEC. It often comes in pairs. Each has an MDIO
>> bus. But to save pins, there are some designs which place two PHYs on
>> one bus, leaving the other empty. The driver unconditionally calls
>> of_mdiobus_register() and if it returns an error, it will error out
>> the probe. So i would not be too surprised if you get reports of
>> missing interfaces with this patch.
> 
> Agreed, the potential for breakage here is too high especially given
> this is fixing a hypothetical problem rather an an actual one. Even if
> we were taking this from the angle of power management, runtime PM
> should ensure that a MDIO bus with no slave, or no activity gets runtime
> suspended.

I understand your points. Thank you for taking time on reviewing this.

Claudiu Beznea

> --
> Florian
>