Re: [EXT] Re: [PATCH net] net: phylink: fix link state on phy-connect

[Russell King - ARM Linux <linux@armlinux.org.uk>]

On Sat, Dec 02, 2017 at 11:08:45AM +0000, Yan Markman wrote:
> Hi Russel
>
> The Grygorii has raised one Additional point (about netif_carrier_off)
> I just didn't want to start before finishing the previous one.
>
> On ifconfig-down the mac_config() called but with LINK=0. 
> The config has no any knowledge what is intention -- up or down and
> should be done under disabled ingress/egress, and so the mac_config
> one of its action is    netif_carrier_off.

With the "p21" patch applied, which is now queued for 4.15-rc by davem,
the behaviour of phylink when phylink_stop() is called becomes entirely
predictable.

When phylink_stop() has been called, provided the carrier state is left
alone, it is guaranteed that mac_link_down() will be called if the link
was originally up, and this will complete prior to phylink_stop()
returning.

After that call has been made, and provided no further calls from the
MAC driver to phylink are made, phylink will make no further calls
to the MAC driver via mac_config(), mac_link_up() or mac_link_down().

It will only resume making these calls once phylink_start() is called.
phylink_start() will cause mac_config() to be called for the current
link mode.  A resolve of the current state is then triggered, which
may trigger further mac_config() calls to be made.  If the link is
then deemed to be up, a call to mac_link_up() will be made.

> After calling mac_config() the phylink checks
>   if (!link  &&  !netif_carrier_ok())
> and decides to abort further down since all-done...

phylink does not contain any such if () statement, so I'm not sure
what code you are referring to.

> REMOVE netif_carrier_off looks like correct BUT has cases where de driver stops to works properly (sorry, I can't remember now what exactly).
> So finally I have placed there the CONDITIONAL carrier-off depending upon link:
> 
> static void mvpp2_mac_config(){
> 	if (state->link)        --- occasionally is TRUE on UP but FALSE on down
> 		netif_carrier_off(port->dev);//YANM

You should not be changing the carrier state in your mac_config()
function, because, again, just like having netif_carrier_off() before
phylink_stop(), it will mess phylink's tracking of the current state
and will cause the mac_link_*() functions to be called erratically.

> BTW: It's seems your below patch should be present anyway.
> +++ b/drivers/net/phy/phylink.c
> @@ -798,6 +798,7 @@ void phylink_disconnect_phy(struct phylink *pl)
> +		pl->phy_state.link = false;

Here's an example without the above on Macchiatobin of a up -> down -> up
sequence on the gigabit wired ethernet port on this board (which I have
bound to a Linux bridge device).  The exact command used for this was:

# ifconfig eth2 down; sleep 2; ifconfig eth2 up

[66926.127009] mvpp2x f4000000.ppv22 eth2: Link is Down
[66926.131557] br0: port 1(eth2) entered disabled state
[66928.144845] mvpp2x f4000000.ppv22 eth2: configuring for inband/sgmii link mode
[66928.144853] mvpp2x f4000000.ppv22 eth2: reconfig: pm 4->4 cm 201->201 f 2->2
[66928.154937] IPv6: ADDRCONF(NETDEV_UP): eth2: link is not ready
[66929.783866] IPv6: ADDRCONF(NETDEV_UP): br0: link is not ready
[66929.979499] IPv6: ADDRCONF(NETDEV_UP): br0: link is not ready
[66931.213407] mvpp2x f4000000.ppv22 eth2: reconfig: pm 4->4 cm 201->201 f a->a
[66931.213424] mvpp2x f4000000.ppv22 eth2: Link is Up - 1Gbps/Full - flow control off
[66931.213433] IPv6: ADDRCONF(NETDEV_CHANGE): eth2: link becomes ready
[66931.213682] br0: port 1(eth2) entered blocking state
[66931.213685] br0: port 1(eth2) entered forwarding state
[66931.213920] IPv6: ADDRCONF(NETDEV_CHANGE): br0: link becomes ready

This is with the "p21" patch applied, and mvpp2x_the netif_carrier_off()
before phylink_stop() in mvpp2x removed.  Basically:

void mv_pp2x_stop_dev(struct mv_pp2x_port *port)
{
        struct gop_hw *gop = &port->priv->hw.gop;
        struct mv_mac_data *mac = &port->mac_data;

        if (port->mac_data.phylink) {
                phylink_stop(port->mac_data.phylink);

                /* Disable interrupts on all CPUs */
                mv_pp2x_port_interrupts_disable(port);
                mv_pp2x_port_napi_disable(port);
                netif_tx_stop_all_queues(port->dev);
        } else {
                /* Stop new packets from arriving to RXQs */
                mv_pp2x_ingress_disable(port);

                mdelay(10);

                /* Disable interrupts on all CPUs */
                mv_pp2x_port_interrupts_disable(port);

                mv_pp2x_port_napi_disable(port);

                netif_carrier_off(port->dev);
                netif_tx_stop_all_queues(port->dev);

                mv_pp2x_egress_disable(port);
        }

        if (port->comphy)
                phy_power_off(port->comphy);

        if (port->priv->pp2_version == PPV21) {
                mv_pp21_port_disable(port);
        } else {
                mv_gop110_port_events_mask(gop, mac);
                mv_gop110_port_disable(gop, mac);
                port->mac_data.flags &= ~MV_EMAC_F_LINK_UP;
                port->mac_data.flags &= ~MV_EMAC_F_PORT_UP;
        }

        if (!port->mac_data.phylink) {
                if (port->mac_data.phy_dev)
                        phy_stop(port->mac_data.phy_dev);
                else
                        tasklet_kill(&port->link_change_tasklet);
        }
}

with the mac_link_down() being:

static void mv_pp22_mac_link_down(struct net_device *dev, unsigned int mode)
{
        struct mv_pp2x_port *port = netdev_priv(dev);

        port->mac_data.link = 0;
        mv_pp2x_ingress_disable(port);
        mv_pp2x_egress_disable(port);
        port->mac_data.flags &= ~MV_EMAC_F_LINK_UP;
}

The phylink case is the same, but with the ingress/egress disable in
a slightly different position - as it would be if the interface were
taken down without the link being up.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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