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: <20220923042037.GA10101@wunner.de>
Date:   Fri, 23 Sep 2022 06:20:37 +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 03:11:47PM -0700, Florian Fainelli wrote:
> 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.

I've just submitted a fix so that at least v6.0 doesn't get released
with a false-positive WARN splat on resume:

https://lore.kernel.org/netdev/8128fdb51eeebc9efbf3776a4097363a1317aaf1.1663905575.git.lukas@wunner.de/

I guess we can look into making the state setting more logical in a
separate step.


> > > 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.

I've interpreted that as an Acked-by for exempting PHY_UP.
If that was not what you wanted, please speak up.

Thanks,

Lukas