netdev - Re: [PATCH net] net: dsa: felix: break at first CPU port during init and teardown

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Date:   Fri, 24 Sep 2021 12:54:22 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH net] net: dsa: felix: break at first CPU port during init
 and teardown

On Thu, Sep 23, 2021 at 07:26:41PM +0300, Vladimir Oltean wrote:
> The NXP LS1028A switch has two Ethernet ports towards the CPU, but only
> one of them is capable of acting as an NPI port at a time (inject and
> extract packets using DSA tags).
> 
> However, using the alternative ocelot-8021q tagging protocol, it should
> be possible to use both CPU ports symmetrically, but for that we need to
> mark both ports in the device tree as DSA masters.
> 
> In the process of doing that, it can be seen that traffic to/from the
> network stack gets broken, and this is because the Felix driver iterates
> through all DSA CPU ports and configures them as NPI ports. But since
> there can only be a single NPI port, we effectively end up in a
> situation where DSA thinks the default CPU port is the first one, but
> the hardware port configured to be an NPI is the last one.
> 
> I would like to treat this as a bug, because if the updated device trees
> are going to start circulating, it would be really good for existing
> kernels to support them, too.
> 
> Fixes: adb3dccf090b ("net: dsa: felix: convert to the new .change_tag_protocol DSA API")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> ---

I will send a v2 for this patch, please discard.