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.

Have you tried putting phylink_stop in .suspend, and phylink_start in .resume?

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.

Fixes: 46f69ded988d ("net: stmmac: Use resolved link config in mac_link_up()")
Signed-off-by: Joakim Zhang <redacted>
---

Broken patch cannot be reverted directly, so manually modified it.

I also tried to fix in other ways, but failed to find a better solution,
any suggestions would be appreciated. Thanks.

Joakim

Do you know exactly why it used to work prior to this patch?