netdev - Re: [PATCH V1 net-next 0/3] net: stmmac: implement clocks

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Message-ID: <YDeiqACL9Rtja6tH@lunn.ch>
Date:   Thu, 25 Feb 2021 14:14:16 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Joakim Zhang <qiangqing.zhang@....com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        netdev <netdev@...r.kernel.org>, dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH V1 net-next 0/3] net: stmmac: implement clocks

> Hi Andrew,
> 
> Thanks for you explanation, I still don't quite understand what the use case it is, could you give me more details, thanks a lot!
> AFAIK now, there are two connections methods, we can abstract the layer:
> 	MAC <-> MAC, there is no PHY attached. It seems to know as Fixed link, right?

Yes, this is the most common way of connecting a switch.

> 	MAC+PHY <-> PHY+MAC

Switches can be connected like this, but not often. Why pay for two
PHYs which you do not need?

> From your expression, you should use an external Ethernet switch, if
> yes, why Ethernet switch needs to use MDIO bus to access another
> MAC's(STMMAC) PHY?

The switch is on the same board as the MAC. Take a look at:
https://netdevconf.info/2.1/papers/distributed-switch-architecture.pdf

It explains the DSA architecture.

   Andrew