Date:   Thu, 2 Sep 2021 11:15:43 +0000
From:   Joakim Zhang <qiangqing.zhang@....com>
To:     Russell King <linux@...linux.org.uk>,
        "andrew@...n.ch" <andrew@...n.ch>
CC:     Vladimir Oltean <olteanv@...il.com>,
        "peppe.cavallaro@...com" <peppe.cavallaro@...com>,
        "alexandre.torgue@...s.st.com" <alexandre.torgue@...s.st.com>,
        "joabreu@...opsys.com" <joabreu@...opsys.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "mcoquelin.stm32@...il.com" <mcoquelin.stm32@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH] net: stmmac: fix MAC not working when system resume back
 with WoL enabled


Hi Russell,

> -----Original Message-----
> From: Russell King <linux@...linux.org.uk>
> Sent: 2021年9月2日 18:50
> To: Joakim Zhang <qiangqing.zhang@....com>
> Cc: Vladimir Oltean <olteanv@...il.com>; peppe.cavallaro@...com;
> alexandre.torgue@...s.st.com; joabreu@...opsys.com;
> davem@...emloft.net; kuba@...nel.org; mcoquelin.stm32@...il.com;
> netdev@...r.kernel.org; andrew@...n.ch; f.fainelli@...il.com;
> hkallweit1@...il.com; dl-linux-imx <linux-imx@....com>
> Subject: Re: [PATCH] net: stmmac: fix MAC not working when system resume
> back with WoL enabled
> 
> On Thu, Sep 02, 2021 at 10:26:13AM +0000, Joakim Zhang wrote:
> >
> > Hi Russell,
> >
> > Thanks a lot!
> >
> > > -----Original Message-----
> > > From: Russell King <linux@...linux.org.uk>
> > > Sent: 2021年9月2日 16:32
> > > To: Joakim Zhang <qiangqing.zhang@....com>
> > > Cc: Vladimir Oltean <olteanv@...il.com>; peppe.cavallaro@...com;
> > > alexandre.torgue@...s.st.com; joabreu@...opsys.com;
> > > davem@...emloft.net; kuba@...nel.org; mcoquelin.stm32@...il.com;
> > > netdev@...r.kernel.org; andrew@...n.ch; f.fainelli@...il.com;
> > > hkallweit1@...il.com; dl-linux-imx <linux-imx@....com>
> > > Subject: Re: [PATCH] net: stmmac: fix MAC not working when system
> > > resume back with WoL enabled
> > >
> > > On Thu, Sep 02, 2021 at 07:28:44AM +0000, Joakim Zhang wrote:
> > > >
> > > > Hi Russell,
> > > >
> > > > > -----Original Message-----
> > > > > From: Russell King <linux@...linux.org.uk>
> > > > > Sent: 2021年9月1日 21:26
> > > > > To: Joakim Zhang <qiangqing.zhang@....com>
> > > > > Cc: Vladimir Oltean <olteanv@...il.com>; peppe.cavallaro@...com;
> > > > > alexandre.torgue@...s.st.com; joabreu@...opsys.com;
> > > > > davem@...emloft.net; kuba@...nel.org;
> mcoquelin.stm32@...il.com;
> > > > > netdev@...r.kernel.org; andrew@...n.ch; f.fainelli@...il.com;
> > > > > hkallweit1@...il.com; dl-linux-imx <linux-imx@....com>
> > > > > Subject: Re: [PATCH] net: stmmac: fix MAC not working when
> > > > > system resume back with WoL enabled
> > > > >
> > > > > This means you need to have the phy <-> mac link up during
> > > > > suspend, and in that case, yes, you do not want to call
> > > > > phylink_stop() or phylink_start().
> > > >
> > > > I have a question here, why need to have the phy<->mac link up
> > > > during
> > > suspend?
> > >
> > > You need the link up because I think from reading the code, it is
> > > _not_ the PHY that is triggering the wakeup in the configuration you are
> using, but the MAC.
> > >
> > > If the link is down, the PHY can't pass the received packet to the
> > > MAC, and the MAC can't recognise the magic packet.
> >
> > Per my understanding, if use PHY-based wakeup, PHY should be active,
> > and MAC can be totally suspended. When PHY receive the magic packets,
> > it will generate a signal via wakeup PIN (PHY seems all have such PIN) to
> inform SoC, we can use this to wake up the system.
> > Please correct me if I misunderstand.
> 
> Correct.
> 
> > > FEC doesn't have this. FEC relies purely on the PHY detecting the
> > > magic packet, which is much more power efficient, because it means
> > > the MAC doesn't need to be powered up and operational while the rest of
> the system is suspended.
> >
> > AFAIK, FEC also use the MAC-based wakeup, when enable FEC WoL feature,
> > it will keep MAC receive logic active, PHY pass the received packets
> > to MAC, if MAC detects the magic packets, it will generate an interrupt to
> wake up the system.
> 
> You're right.
> 
> However, as the PHY is not configured for WoL with FEC, and
> fec_suspend() unconditionally calls phy_stop() which will place the PHY into
> suspend mode. 

No, phylib has much logic to avoid putting PHY into suspended state if either MAC or
PHY WoL active. Such as in phy_suspend(),
	if (wol.wolopts || (netdev && netdev->wol_enabled))
		return -EBUSY;

Or in mdio_bus_phy_may_suspend()...

> Maybe the PHY driver there has a NULL phydrv->suspend
> method? However, I see that at803x has suspend methods (which I believe is
> the PHY that gets used with i.MX products) which will power down the PHY.

Yes, we have many boards use AR8031 PHY, and all support MAC-based wakeup feature.

> So, how does this work with FEC - because right now I can't see it working, but
> you say it does.
>
> I think we need to understand how FEC is working here, and we need a deeper
> understanding why stmmac isn't working.

Emm, @andrew@...n.ch, Andrew is much familiar with FEC, and PHY maintainers,
Could you please help put insights here if possible?

> I don't have any iMX systems that support WoL, so this isn't something I can
> test. (SolidRun's i.MX platforms do not support any kind of system power down,
> so suspend isn't supported.)

Understood, thanks.

Best Regards,
Joakim Zhang

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