Subject: Re: [PATCH 2/2] net: ethernet: Add driver for Sunplus SP7021

From: Andrew Lunn <[email-masked]>
Date: Mon, 8 Nov 2021 14:15:49 +0100

> SP7021 Ethernet supports 3 operation modes:
>  - Dual Ethernet mode
>    In this mode, driver creates two net-device interfaces. Each connects
>    to PHY. There are two LAN ports totally.
>    I am sorry that EMAC of SP7021 cannot support L2 switch functions
>    of Linux switch-device model because it only has partial function of 
>    switch.

This is fine.

> 
>  - One Ethernet mode
>    In this mode, driver creates one net-device interface. It connects to
>    to a PHY (There is only one LAN port).
>    The LAN port is then connected to a 3-port Ethernet hub.
>    The 3-port Ethernet hub is a hardware circuitry. All operations 
>    (packet forwarding) are done by hardware. No software 
>    intervention is needed. Actually, even just power-on, no software 
>    running, two LAN ports of SP7021 work well as 2-port hub.

We need to dig into the details of this mode. I would initially say
no, until we really do know it is impossible to do it correctly.  Even
if it is impossible to do it correctly, i'm still temped to reject
this mode.

How does spanning tree work? Who sends and receives the BPDU?

Is there PTP support? How do you send and receive the PTP frames?

Is IGMP snooping supported?

All of these have one thing in common, you need to be able to egress
frames out a specific port of the switch, and you need to know what
port a received frames ingressed on. If you can do that, you can
probably do proper support in Linux.

Is the datasheet available?

   Andrew