Subject: Re: [RFC PATCH net-next 3/8] net: phy: Allow PHY devices to identify themselves as Ethernet switches

From: Andrew Lunn <[email-masked]>
Date: Thu, 30 Apr 2015 19:16:30 +0200

> > Hi Florian
> > 
> > I have another two use cases for fixed_phy which i'm thinking about
> > implementing soon. Both require putting a fixed_phy into DSA port
> > properties in DT.
> > 
> > The first is when the CPU ethernet and the switch don't have the same
> > speed capabilities. At the moment, the switch driver configures the
> > CPU port to its maximum speed. But i know of a board coming soon with
> > gigabit switch ports, but the CPU Ethernet is only fast Ethernet.
> 
> With the patch after, if your switch is MDIO connected to your host, you
> could make that happen easily, since the read_status() callback would
> only be invoked for the CPU port from the CPU Ethernet MAC driver
> (that's the theory).

I'm not sure i get what you are saying.

What we currently have is:

CPU ETH->fixed_phy                      Switch port CPU
|                                       |
+---------------------------------------+

and what i'm thinking we want is:

CPU ETH->fixed_phy          fixed_phy <-Switch port CPU
|                                       |
+---------------------------------------+

So that when setting up the switch side of the link, i can read from
the switch ports fixed_phy how the port should be configured.

I'm also wondering if they could even share one fixed_phy? 
But i suspect that will not work.

> > So in this respect, i'm wondering if is_switch is the best of names?
> 
> Probably not, I agree, pseudo_fixed_link ;)?

Yes, something like that.

     Andrew