netdev - Re: [PATCH net-next v2 2/3] net: dsa: mv88e6xxx: add support for bridge flags

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Date:   Tue, 19 Feb 2019 23:34:08 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Vivien Didelot <vivien.didelot@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v2 2/3] net: dsa: mv88e6xxx: add support for
 bridge flags

On Tue, Feb 19, 2019 at 05:00:59PM +0000, Russell King - ARM Linux admin wrote:
> I've just changed my last patch to set these modes from
> dsa_port_bridge_join() and dsa_port_bridge_leave(), and while testing,
> I notice this on the ZII rev B board:
> 
> At boot (without anything connected to any of the switch ports):
> 
> br0: port 1(lan0) entered blocking state
> br0: port 1(lan0) entered disabled state
> device lan0 entered promiscuous mode
> device eth1 entered promiscuous mode
> br0: port 2(lan1) entered blocking state
> br0: port 2(lan1) entered disabled state
> device lan1 entered promiscuous mode
> ...
> 
> I then removed lan0 from the bridge:
> 
> device lan0 left promiscuous mode
> br0: port 1(lan0) entered disabled state
> 
> and then added it back:
> 
> br0: port 1(lan0) entered blocking state
> br0: port 1(lan0) entered disabled state
> device lan0 entered promiscuous mode
> 
> Now, you'd expect lan0 and lan1 to be configured the same at this
> point, and the same as it was before lan0 was removed from the bridge?
> lan0 is port 0, lan1 is port 1 on this switch - and the register debug
> says:
> 
>     GLOBAL GLOBAL2 SERDES     0    1    2    3    4    5    6
>  0:  c800       0    1140  500f 500f 500f 500f 500f 4e07 4d04
> ...
>  4:  40a8     258     1e0   43c  43d  43d   7c  430  53f 373f
> 
> Note that port 0 is in disabled state, but port 1 and 2 are in
> blocking state... but wait, the kernel printed a message saying it was
> in disabled state!
> 
> If I do the same for lan1, port 1 above changed from 0x43d to 0x433 as
> expected, and then returns to 0x43c.
> 
> It looks like DSA isn't always in sync with bridge as per port state.

Okay, the problem is what we do when we up the port.

When the port is added to the bridge device, and it's down, the bridge
code sets the STP state to "disabled".

Then when we up the interface, dsa_slave_open() calls dsa_port_enable(),
which then decides to change the STP state on its own without reference
to the state assigned by net/bridge:

int dsa_port_enable(struct dsa_port *dp, struct phy_device *phy)
{
        u8 stp_state = dp->bridge_dev ? BR_STATE_BLOCKING : BR_STATE_FORWARDING;
...
        dsa_port_set_state_now(dp, stp_state);
...
}

I can understand setting the state to BR_STATE_FORWARDING for
stand-alone ports, but why for bridged ports when the bridge code has
already taken care of configuring the STP state of the port?

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