netdev - Re: [PATCH AUTOSEL 6.0 11/77] net: dsa: all DSA masters must be down when changing the tagging protocol

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Date:   Mon, 10 Oct 2022 14:54:30 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Vladimir Oltean <vladimir.oltean@....com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Paolo Abeni <pabeni@...hat.com>, andrew@...n.ch,
        vivien.didelot@...il.com, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, netdev@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 6.0 11/77] net: dsa: all DSA masters must be down
 when changing the tagging protocol

On Sun, Oct 09, 2022 at 06:06:48PM -0400, Sasha Levin wrote:
> From: Vladimir Oltean <vladimir.oltean@....com>
> 
> [ Upstream commit f41ec1fd1c20e2a4e60a4ab8490b3e63423c0a8a ]
> 
> The fact that the tagging protocol is set and queried from the
> /sys/class/net/<dsa-master>/dsa/tagging file is a bit of a quirk from
> the single CPU port days which isn't aging very well now that DSA can
> have more than a single CPU port. This is because the tagging protocol
> is a switch property, yet in the presence of multiple CPU ports it can
> be queried and set from multiple sysfs files, all of which are handled
> by the same implementation.
> 
> The current logic ensures that the net device whose sysfs file we're
> changing the tagging protocol through must be down. That net device is
> the DSA master, and this is fine for single DSA master / CPU port setups.
> 
> But exactly because the tagging protocol is per switch [ tree, in fact ]
> and not per DSA master, this isn't fine any longer with multiple CPU
> ports, and we must iterate through the tree and find all DSA masters,
> and make sure that all of them are down.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---

Not needed for stable kernels, please drop, thanks.