netdev - Re: Problem with PHY state machine when using interrupts

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Message-ID: <62085f48-df18-f987-f521-dcdfbd7f574b@gmail.com>
Date:   Mon, 24 Jul 2017 15:36:11 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Mason <slash.tmp@...e.fr>, Andrew Lunn <andrew@...n.ch>,
        Mans Rullgard <mans@...sr.com>
Cc:     netdev <netdev@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: Problem with PHY state machine when using interrupts

On 07/24/2017 02:20 PM, Mason wrote:
> On 24/07/2017 21:53, Florian Fainelli wrote:
> 
>> Well now that I see the possible interrupts generated, I indeed don't
>> see how you can get a link down notification unless you somehow force
>> the link down yourself, which would certainly happen in phy_suspend()
>> when we set BMCR.pwrdwn, but that may be too late.
>>
>> You should still expect the adjust_link() function to be called though
>> with PHY_HALTED being set and that takes care of doing phydev->link = 0
>> and netif_carrier_off(). If that still does not work, then see whether
>> removing the call to phy_stop() does help (it really should).
> 
> The only functions setting phydev->state to PHY_HALTED
> are phy_error() and phy_stop() AFAICT.
> 
> I am aware that when phy_state_machine() handles the
> PHY_HALTED state, it will set phydev->link = 0;
> and call netif_carrier_off() -- because that's where
> I copied that code from.
> 
> My issue is that phy_state_machine() does not run when
> I run 'ip set link dev eth0 down' from the command line.

Yes, that much is clear, which is why I suggested earlier you try the
patch at the end now.

> 
> If I'm reading the code right, phy_disconnect() actually
> stops the state machine.
> 
> In interrupt mode, phy_state_machine() doesn't run
> because no interrupt is generated.
> 
> In polling mode, phy_state_machine() doesn't run
> because phy_disconnect() stops the state machine.
> 
> Introducing a sleep before phy_disconnect() gives
> the state machine a chance to run in polling mode,
> but it doesn't feel right, and doesn't fix the
> other mode, which I'm using.

There are several problems it seems:

- the PHY state machine cannot move solely based on the PHY generating
interrupts during phy_stop() if none of the changing conditions for the
HW have changed, come to think about it, I doubt any PHY would be
capable of doing something like that

- there is an expectation from your driver to have adjust_link() run
sometime during ndo_stop() to do something, but why?

What is special about nb8800 that interrupts should be generated during
ndo_stop(), and why do you think this is going to solve your problem?

> 
> Looking at bcm_enet_stop() it calls phy_stop() and
> phy_disconnect() just like the nb8800 driver...
> 
> I'm stumped.

My suggestion of not using phy_stop() was not a good one, but
functionally there is little difference in doing phy_stop() +
phy_disconnect() or just phy_disconnect() alone. What matters is that we
restart the PHY properly when phy_connect() or phy_start() is called.

What I understand now from your "bug report" is that you want
adjust_link to run with phydev->link = 0 to do something during
ndo_close() but you have not explained why, but I suspect such that upon
ndo_open() things work again.

What I suspect your bug is, is that the really was no change in link
status, no interrupt was generated because there should not be one, yet
some of what nb8800_stop() does is not properly balanced by
nb8800_open(). How about the following patch:

diff --git a/drivers/net/ethernet/aurora/nb8800.c
b/drivers/net/ethernet/aurora/nb8800.c
index 041cfb7952f8..b07dea3ab019 100644
--- a/drivers/net/ethernet/aurora/nb8800.c
+++ b/drivers/net/ethernet/aurora/nb8800.c
@@ -972,6 +972,10 @@ static int nb8800_open(struct net_device *dev)
        nb8800_mac_rx(dev, true);
        nb8800_mac_tx(dev, true);

+       priv->speed = -1;
+       priv->link = -1;
+       priv->duplex = -1;
+
        phydev = of_phy_connect(dev, priv->phy_node,
                                nb8800_link_reconfigure, 0,
                                priv->phy_mode);
-- 
Florian