RE: [PATCH] net: stmmac: fix MAC not working when system resume back with WoL enabled

Hi Russell,

-----Original Message-----
From: Russell King <linux@armlinux.org.uk>
Sent: 2021年9月2日 18:50
To: Joakim Zhang <redacted>
Cc: Vladimir Oltean <olteanv@gmail.com>; peppe.cavallaro@st.com;
alexandre.torgue@foss.st.com; joabreu@synopsys.com;
davem@davemloft.net; kuba@kernel.org; mcoquelin.stm32@gmail.com;
netdev@vger.kernel.org; andrew@lunn.ch; f.fainelli@gmail.com;
hkallweit1@gmail.com; dl-linux-imx [off-list ref]
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:

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Hi Russell,

Thanks a lot!

quoted

-----Original Message-----
From: Russell King <linux@armlinux.org.uk>
Sent: 2021年9月2日 16:32
To: Joakim Zhang <redacted>
Cc: Vladimir Oltean <olteanv@gmail.com>; peppe.cavallaro@st.com;
alexandre.torgue@foss.st.com; joabreu@synopsys.com;
davem@davemloft.net; kuba@kernel.org; mcoquelin.stm32@gmail.com;
netdev@vger.kernel.org; andrew@lunn.ch; f.fainelli@gmail.com;
hkallweit1@gmail.com; dl-linux-imx [off-list ref]
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:

quoted

Hi Russell,

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-----Original Message-----
From: Russell King <linux@armlinux.org.uk>
Sent: 2021年9月1日 21:26
To: Joakim Zhang <redacted>
Cc: Vladimir Oltean <olteanv@gmail.com>; peppe.cavallaro@st.com;
alexandre.torgue@foss.st.com; joabreu@synopsys.com;
davem@davemloft.net; kuba@kernel.org;

mcoquelin.stm32@gmail.com;

quoted

quoted

quoted

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netdev@vger.kernel.org; andrew@lunn.ch; f.fainelli@gmail.com;
hkallweit1@gmail.com; dl-linux-imx [off-list ref]
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.

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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.

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Please correct me if I misunderstand.

Correct.

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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.

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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@lunn.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