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1日 17:14
To: Joakim Zhang <redacted>
Cc: 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 Wed, Sep 01, 2021 at 05:02:28PM +0800, Joakim Zhang wrote:

quoted

We can reproduce this issue with below steps:
1) enable WoL on the host
2) host system suspended
3) remote client send out wakeup packets We can see that host system
resume back, but can't work, such as ping failed.

After a bit digging, this issue is introduced by the commit
46f69ded988d
("net: stmmac: Use resolved link config in mac_link_up()"), which use
the finalised link parameters in mac_link_up() rather than the
parameters in mac_config().

There are two scenarios for MAC suspend/resume:

1) MAC suspend with WoL disabled, stmmac_suspend() call
phylink_mac_change() to notify phylink machine that a change in MAC
state, then .mac_link_down callback would be invoked. Further, it will
call phylink_stop() to stop the phylink instance. When MAC resume
back, firstly phylink_start() is called to start the phylink instance,
then call phylink_mac_change() which will finally trigger phylink
machine to invoke .mac_config and .mac_link_up callback. All is fine
since configuration in these two callbacks will be initialized.

2) MAC suspend with WoL enabled, phylink_mac_change() will put link
down, but there is no phylink_stop() to stop the phylink instance, so
it will link up again, that means .mac_config and .mac_link_up would
be invoked before system suspended. After system resume back, it will
do DMA initialization and SW reset which let MAC lost the hardware
setting (i.e MAC_Configuration register(offset 0x0) is reset). Since
link is up before system suspended, so .mac_link_up would not be
invoked after system resume back, lead to there is no chance to
initialize the configuration in .mac_link_up callback, as a result,
MAC can't work any longer.

Above description is what I found when debug this issue, this patch is
just revert broken patch to workaround it, at least make MAC work when
system resume back with WoL enabled.

Said this is a workaround, since it has not resolve the issue completely.
I just move the speed/duplex/pause etc into .mac_config callback,
there are other configurations in .mac_link_up callback which also
need to be initialized to work for specific functions.

NAK. Please read the phylink documentation. speed/duplex/pause is undefined
in .mac_config.

Speed/duplex/pause also the field of " struct phylink_link_state", so these can be refered in .mac_config, please
see the link which stmmac did before:
https://elixir.bootlin.com/linux/v5.4.143/source/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c#L852

I think the problem here is that you're not calling phylink_stop() when WoL is
enabled, which means phylink will continue to maintain the state as per the
hardware state, and phylib will continue to run its state machine reporting the
link state to phylink.

Yes, I also tried do below code change, but the host would not be wakeup, phylink_stop() would
call phy_stop(), phylib would call phy_suspend() finally, it will not suspend phy if it detect WoL enabled,
so now I don't know why system can't be wakeup with this code change.

@@ -5374,7 +5374,6 @@ int stmmac_suspend(struct device *dev)
                rtnl_lock();
                if (device_may_wakeup(priv->device))
                        phylink_speed_down(priv->phylink, false);
-               phylink_stop(priv->phylink);
                rtnl_unlock();
                mutex_lock(&priv->lock);

@@ -5385,6 +5384,10 @@ int stmmac_suspend(struct device *dev)
        }
        mutex_unlock(&priv->lock);

+       rtnl_lock();
+       phylink_stop(priv->phylink);
+       rtnl_unlock();
+
        priv->speed = SPEED_UNKNOWN;
        return 0;
 }

@@ -5448,6 +5451,12 @@ int stmmac_resume(struct device *dev)
                pinctrl_pm_select_default_state(priv->device);
                if (priv->plat->clk_ptp_ref)
                        clk_prepare_enable(priv->plat->clk_ptp_ref);
+
+               rtnl_lock();
+               /* We may have called phylink_speed_down before */
+               phylink_speed_up(priv->phylink);
+               rtnl_unlock();
+
                /* reset the phy so that it's ready */
                if (priv->mii && priv->mdio_rst_after_resume)
                        stmmac_mdio_reset(priv->mii);

@@ -5461,13 +5470,9 @@ int stmmac_resume(struct device *dev)
                        return ret;
        }

-       if (!device_may_wakeup(priv->device) || !priv->plat->pmt) {
-               rtnl_lock();
-               phylink_start(priv->phylink);
-               /* We may have called phylink_speed_down before */
-               phylink_speed_up(priv->phylink);
-               rtnl_unlock();
-       }
+       rtnl_lock();
+       phylink_start(priv->phylink);
+       rtnl_unlock();

        rtnl_lock();
        mutex_lock(&priv->lock);

phylink_stop() (and therefore phy_stop()) should be called even if WoL is active
to shut down this state reporting, as other network drivers do.

Ok, you mean that phylink_stop() also should be called even if WoL is active, I would look in this direction since
you are a professional.

Thanks.

Best Regards,
Joakim Zhang