netdev - Re: [PATCH net-next v2 0/2] net: phy: improve PHY suspend/resume

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Message-ID: <ae4c30a6-7724-a02c-189a-1ff8768528ee@gmail.com>
Date:   Tue, 5 Jun 2018 21:39:37 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2 0/2] net: phy: improve PHY suspend/resume

On 02.06.2018 22:27, Heiner Kallweit wrote:
> On 01.06.2018 02:10, Andrew Lunn wrote:
>>> Configuring the different WoL options isn't handled by writing to
>>> the PHY registers but by writing to chip / MAC registers.
>>> Therefore phy_suspend() isn't able to figure out whether WoL is
>>> enabled or not. Only the parent has the full picture.
>>
>> Hi Heiner
>>
>> I think you need to look at your different runtime PM domains.  If i
>> understand the code right, you runtime suspend if there is no
>> link. But for this to work correctly, your PHY needs to keep working.
>> You also cannot assume all accesses to the PHY go via the MAC. Some
>> calls will go direct to the PHY, and they can trigger MDIO bus
>> accesses.  So i think you need two runtime PM domains. MAC and MDIO
>> bus.  Maybe just the pll? An MDIO bus is a device, so it can have its
>> on PM callbacks. It is not clear what you need to resume in order to
>> make MDIO work.
>>
> Thanks for your comments!
> The actual problem is quite small: I get an error at MDIO suspend,
> the PHY however is suspended later by the driver's suspend callback
> anyway. Because the problem is small I'm somewhat reluctant to
> consider bigger changes like introducing different PM domains.
> 
> Primary reason for the error is that the network chip is in PCI D3hot
> at that moment. In addition to that for some of the chips supported by
> the driver also MDIO-relevant PLL's might be disabled.
> 
> By the way:
> When checking PM handling for PHY/MDIO I stumbled across something
> that can be improved IMO, I'll send a patch for your review.
> 
I experimented a little and with adding Runtime PM to MDIO bus and
PHY device I can make it work:
PHY runtime-resumes before entering suspend and resumes its parent
(MDIO bus) which then resumes its parent (PCI device).
However this needs quite some code and is hard to read / understand
w/o reading through this mail thread.

And in general I still have doubts this is the right way. Let's
consider the following scenario:

A network driver configures WoL in its suspend callback
(incl. setting the device to wakeup-enabled).
The suspend callback of the PHY is called before this and therefore
has no clue that WoL will be configured a little later, with the
consequence that it will do an unsolicited power-down.
The network driver then has to detect this and power-up the PHY again.
This doesn't seem to make much sense and still my best idea is to
establish a mechanism that a device can state: I orchestrate PM
of my children.

Heiner

>> It might also help if you do the phy_connect in .ndo_open and
>> disconnect in .ndo_stop. This is a common pattern in drivers. But some
>> also do it is probe and remove.
>>
> Thanks for the hint. I will move phy_connect_direct accordingly.
> 
>>      Andrew
>>
> Heiner
>