linux-kernel - Re: [PATCH] net: phy: micrel: reconfigure the phy on resume

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Date:   Thu, 11 Feb 2021 13:36:16 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Claudiu.Beznea@...rochip.com, linux@...linux.org.uk,
        andrew@...n.ch, davem@...emloft.net, kuba@...nel.org,
        rjw@...ysocki.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH] net: phy: micrel: reconfigure the phy on resume

On 11.02.2021 13:17, Pavel Machek wrote:
> On Thu 2021-01-14 12:05:21, Heiner Kallweit wrote:
>> On 14.01.2021 11:41, Claudiu.Beznea@...rochip.com wrote:
>>>
>>>
>>> On 14.01.2021 12:25, Russell King - ARM Linux admin wrote:
>>>>
>>>> As I've said, if phylib/PHY driver is not restoring the state of the
>>>> PHY on resume from suspend-to-ram, then that's an issue with phylib
>>>> and/or the phy driver.
>>>
>>> In the patch I proposed in this thread the restoring is done in PHY driver.
>>> Do you think I should continue the investigation and check if something
>>> should be done from the phylib itself?
>>>
>> It was the right move to approach the PM maintainers to clarify whether
>> the resume PM callback has to assume that power had been cut off and
>> it has to completely reconfigure the device. If they confirm this
>> understanding, then:
> 
> Power to some devices can be cut during s2ram, yes.
> 
Thanks for the confirmation.

>> - the general question remains why there's separate resume and restore
>>   callbacks, and what restore is supposed to do that resume doesn't
>>   have to do
> 
> You'll often have same implementation, yes.
> 

If resume and restore both have to assume that power was cut off,
then they have to fully re-initialize the device. Therefore it's still
not clear to me when you would have differing implementations for both
callbacks.

>> - it should be sufficient to use mdio_bus_phy_restore also as resume
>>   callback (instead of changing each and every PHY driver's resume),
>>   because we can expect that somebody cutting off power to the PHY
>>   properly suspends the MDIO bus before
> 
> If restore works with power cut and power not cut then yes, you should
> get away with that.
> 
> Best regards,
> 								Pavel
> 

Heiner