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

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Message-ID: <9f02c173-05db-4607-8caf-13c86035c769@gmail.com>
Date: Mon, 29 Jan 2024 08:54:44 -0800
From: Florian Fainelli <f.fainelli@...il.com>
To: Vladimir Oltean <olteanv@...il.com>
Cc: Luiz Angelo Daros de Luca <luizluca@...il.com>, 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, arinc.unal@...nc9.com, ansuelsmth@...il.com
Subject: Re: [PATCH net-next v4 08/11] net: dsa: realtek: clean user_mii_bus
 setup



On 1/29/2024 8:43 AM, Vladimir Oltean wrote:
> On Mon, Jan 29, 2024 at 08:22:47AM -0800, Florian Fainelli wrote:
>> It does seem however universally acceptable to stop any DMAs and
>> packets from flowing as a default and safe implementation to the
>> upstream kernel.
> 
> DMA I can understand, because you wouldn't want the hardware to notify
> you of a buffer you have no idea about. But DSA doesn't assume that
> switches have DMA, and generally speaking, stopping the offloaded
> traffic path seems unnecessary. It will be stopped when the new kernel
> sets up the interfaces as standalone, renegotiates the link, etc.

Very true, I suppose most driver writers might want to stop the packet 
flow from the source however and simply disable switch ports. There are 
also power management considerations at least there were for some of the 
products I worked with.
-- 
Florian