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

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Message-ID: <20220918205516.GA13914@wunner.de>
Date:   Sun, 18 Sep 2022 22:55:16 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Florian Fainelli <f.fainelli@...il.com>
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 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.


> > 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?

Thanks,

Lukas