netdev - Re: [PATCH net-next v3 5/7] usbnet: smsc95xx: Forward PHY interrupts to PHY driver to avoid polling

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Date:   Sun, 18 Sep 2022 15:11:47 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org,
        linux-usb@...r.kernel.org,
        Steve Glendinning <steve.glendinning@...well.net>,
        UNGLinuxDriver@...rochip.com, Oliver Neukum <oneukum@...e.com>,
        Andre Edich <andre.edich@...rochip.com>,
        Oleksij Rempel <linux@...pel-privat.de>,
        Martyn Welch <martyn.welch@...labora.com>,
        Gabriel Hojda <ghojda@...urs.ro>,
        Christoph Fritz <chf.fritz@...glemail.com>,
        Lino Sanfilippo <LinoSanfilippo@....de>,
        Philipp Rosenberger <p.rosenberger@...bus.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Russell King <linux@...linux.org.uk>,
        Ferry Toth <fntoth@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        'Linux Samsung SOC' <linux-samsung-soc@...r.kernel.org>
Subject: Re: [PATCH net-next v3 5/7] usbnet: smsc95xx: Forward PHY interrupts
 to PHY driver to avoid polling



On 9/18/2022 1:55 PM, Lukas Wunner wrote:
> On Sun, Sep 18, 2022 at 01:41:13PM -0700, Florian Fainelli wrote:
>> On 9/18/2022 12:13 PM, Lukas Wunner wrote:
>>> On Mon, Aug 29, 2022 at 01:40:05PM +0200, Marek Szyprowski wrote:
>>>> I've finally traced what has happened. I've double checked and indeed
>>>> the 1758bde2e4aa commit fixed the issue on next-20220516 kernel and as
>>>> such it has been merged to linus tree. Then the commit 744d23c71af3
>>>> ("net: phy: Warn about incorrect mdio_bus_phy_resume() state") has been
>>>> merged to linus tree, which triggers a new warning during the
>>>> suspend/resume cycle with smsc95xx driver. Please note, that the
>>>> smsc95xx still works fine regardless that warning. However it look that
>>>> the commit 1758bde2e4aa only hide a real problem, which the commit
>>>> 744d23c71af3 warns about.
>>>>
>>>> Probably a proper fix for smsc95xx driver is to call phy_stop/start
>>>> during suspend/resume cycle, like in similar patches for other drivers:
>>>>
>>>> https://lore.kernel.org/all/20220825023951.3220-1-f.fainelli@gmail.com/
>>>
>>> No, smsc95xx.c relies on mdio_bus_phy_{suspend,resume}() and there's
>>> no need to call phy_{stop,start}() >
>>> 744d23c71af3 was flawed and 6dbe852c379f has already fixed a portion
>>> of the fallout.
>>>
>>> However the WARN() condition still seems too broad and causes false
>>> positives such as in your case.  In particular, mdio_bus_phy_suspend()
>>> may leave the device in PHY_UP state, so that's a legal state that
>>> needs to be exempted from the WARN().
>>
>> How is that a legal state when the PHY should be suspended? Even if we are
>> interrupt driven, the state machine should be stopped, does not mean that
>> Wake-on-LAN or other activity interrupts should be disabled.
> 
> mdio_bus_phy_suspend()
>    phy_stop_machine()
>      phydev->state = PHY_UP  #  if (phydev->state >= PHY_UP)
> 
> So apparently PHY_UP is a legal state for a suspended PHY.

It is not clear to me why, however. Sure it does ensure that when we 
resume we set needs_aneg = true but this feels like a hack in the sense 
that we are setting the PHY in a provisional state in anticipation for 
what might come next.

> 
> 
>>> Does the issue still appear even after 6dbe852c379f?
>>>
>>> If it does, could you test whether exempting PHY_UP silences the
>>> gratuitous WARN splat?  I.e.:
>>
>> If you allow PHY_UP, then the warning becomes effectively useless, so I
>> don't believe this is quite what you want to do here.
> 
> Hm, maybe the WARN() should be dropped altogether?

And then be left with debugging similar problems that prompted me to 
submit the patch in the first place, no thank you. I guess I would 
rather accept that PHY_UP needs to be special cased then.
-- 
Florian