netdev - Re: [PATCH net] net: dsa: fix unintended change of bridge interface STP state

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Date:   Wed, 20 Feb 2019 10:38:05 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Russell King <rmk+kernel@...linux.org.uk>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net] net: dsa: fix unintended change of bridge interface
 STP state

On 2/20/19 9:27 AM, Andrew Lunn wrote:
> On Wed, Feb 20, 2019 at 09:22:30AM -0800, Florian Fainelli wrote:
>> On 2/20/19 2:32 AM, Russell King wrote:
>>> When a DSA port is added to a bridge and brought up, the resulting STP
>>> state programmed into the hardware depends on the order that these
>>> operations are performed.  However, the Linux bridge code believes that
>>> the port is in disabled mode.
>>>
>>> If the DSA port is first added to a bridge and then brought up, it will
>>> be in blocking mode.  If it is brought up and then added to the bridge,
>>> it will be in disabled mode.
>>>
>>> This difference is caused by DSA always setting the STP mode in
>>> dsa_port_enable() whether or not this port is part of a bridge.  Since
>>> bridge always sets the STP state when the port is added, brought up or
>>> taken down, it is unnecessary for us to manipulate the STP state.
>>>
>>> Apparently, this code was copied from Rocker, and the very next day a
>>> similar fix for Rocker was merged but was not propagated to DSA.  See
>>> e47172ab7e41 ("rocker: put port in FORWADING state after leaving bridge")
>>>
>>> Fixes: b73adef67765 ("net: dsa: integrate with SWITCHDEV for HW bridging")
>>> Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>
>>
>> Nice example of cargo cult programming, thanks for fixing this!
> 
> Maybe now would be a good time to look at other drivers. Does the
> Microsemi Ocelot driver have the same issue?

Checked fsl-dpaa2/ethsw and ocelot and neither of those seem to be
affected by this problem.
-- 
Florian