linux-kernel - RE: [PATCH 2/2] net: ethernet: Add driver for Sunplus SP7021

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Message-ID: <da39cce70a2849799bfff07394e27b0d@sphcmbx02.sunplus.com.tw>
Date:   Tue, 9 Nov 2021 17:05:01 +0000
From:   Wells Lu 呂芳騰 <wells.lu@...plus.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     Wells Lu <wellslutw@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>
Subject: RE: [PATCH 2/2] net: ethernet: Add driver for Sunplus SP7021

> > I don't know how to implement STP in L2 switch like SP7021.
> 
> That is the nice thing about using Linux. It already knows how to implement
> STP. The bridge will do it for you. You just need to add the callbacks in the
> driver which are needed. Please take a look at other switchdev drivers.
> 
> > If this is acceptable, I'd like to have Ethernet of SP7021 have two
> > operation
> > modes:
> >  - Dual NIC mode
> >  - Single NIC with 2-port frame-flooding hub mode
> 
> No, sorry. Do it correctly, or do not do it. Please start with a clean driver doing
> Dual NIC mode. You can add L2 support later, once you have done the research
> to understand switchdev, etc.

Sorry, I will go with Dual NIC mode. I'll do a whole cleanup on driver for this.
Please kindly review again.

I need time to study more about switchdev and propose a plan to high
management of company. However, Sunplus is not a networking company, 
but targets on Linux-based industrial control, autonomous mobile robot, ...


> > RMII pins of PHY ports of SP7021 are multiplexable. I'd like to switch
> > RMII pins of the second PHY for other use if single NIC mode is used.
> > In fact, some SP7021 boards have dual Ethernet and some have only one
> > Ethernet. We really need the two operation modes.
> 
> Only using a subset of ports in a switch is common. The common binding for
> DSA switches is described in:
> 
> Documentation/devicetree/bindings/net/dsa/dsa.yaml and for example
> Documentation/devicetree/bindings/net/dsa/hirschmann,hellcreek.yaml is a
> memory mapped switch. Notice the reg numbers:
> 
>            ethernet-ports {
>                 #address-cells = <1>;
>                 #size-cells = <0>;
> 
>                 port@0 {
>                     reg = <0>;
>                     label = "cpu";
>                     ethernet = <&gmac0>;
>                 };
> 
>                 port@2 {
>                     reg = <2>;
>                     label = "lan0";
>                     phy-handle = <&phy1>;
>                 };
> 
> reg = <1> is missing in this example. Port 1 of the switch is not used. You can
> do the same with a 2 port switch, when you don't want to make use of a port.
> Just don't list it in DT.

Thank you for routing me to the document.
Now I know there are switch device examples in folder dsa/.
We can refer to them when we want to make a switch.


> > After looking up some data, I find RMC means reserved multi-cast.
> > RMC packets means packets with DA = 0x0180c2000000, 0x0180c2000002 ~
> > 0x0180c200000f, except the PAUSE packet (DA = 0x0180c2000001)
> 
> Ah, good. BPDUs use 01:80:C2:00:00:00. So they will be passed when the port is
> in blocking mode. PTP uses 01:80:C2:00:00:0E. So the hardware designers
> appear to of designed a proper L2 switch with everything you need for a
> managed switch. What is missing is software. The more i learn about this
> hardware, the more i've convinced you need to write proper Linux support for
> it, not your mode hacks.
> 
>     Andrew

Thanks for confirming that the L2 switch is good enough for switch device.
Actually, the IP was licensed from other company long ago. We don’t know 
all details.