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

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Date:   Wed, 1 Sep 2021 10:13:32 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Joakim Zhang <qiangqing.zhang@....com>
Cc:     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, linux-imx@....com
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:
> 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.

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.

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.

Thanks.

-- 
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