netdev - Re: [PATCH net-next v4 08/11] net: dsa: realtek: clean user_mii

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Message-ID: <a50ca71f-e0b9-43ad-a08f-b4ee8a349387@arinc9.com>
Date: Tue, 30 Jan 2024 17:40:26 +0300
From: Arınç ÜNAL <arinc.unal@...nc9.com>
To: Florian Fainelli <f.fainelli@...il.com>,
 Vladimir Oltean <olteanv@...il.com>,
 Luiz Angelo Daros de Luca <luizluca@...il.com>
Cc: netdev@...r.kernel.org, linus.walleij@...aro.org, alsi@...g-olufsen.dk,
 andrew@...n.ch, davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, ansuelsmth@...il.com
Subject: Re: [PATCH net-next v4 08/11] net: dsa: realtek: clean user_mii_bus
 setup

On 29.01.2024 19:22, Florian Fainelli wrote:
> 
> 
> On 1/29/2024 8:15 AM, Vladimir Oltean wrote:
>>  From other discussions I've had, there seems to be interest in quite the
>> opposite thing, in fact. Reboot the SoC running Linux, but do not
>> disturb traffic flowing through the switch, and somehow pick up the
>> state from where the previous kernel left it.
> 
> Yes this is actually an use case that is very dear to the users of DSA in an airplane. The entertainment system in the seat in front of you typically has a left, CPU/display and right set of switch ports. Across the 300+ units in the plane each entertainment systems runs STP to avoid loops being created when one of the display units goes bad. Occasionally cabin crew members will have to swap those units out since they tend to wear out. When they do, the switch operates in a headless mode and it would be unfortunate that plugging in a display unit into the network again would be disrupting existing traffic. I have seen out of tree patches doing that, but there was not a good way to make them upstream quality.

This piqued my interest. I'm trying to understand how exactly plugging in a
display unit into the network would disrupt the traffic flow. Is this about
all network interfaces attached to the bridge interface being blocked when
a new link is established to relearn the changed topology?

Arınç