Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Mon, 10 Jun 2019 23:11:33 +0200
From:   Andrew Lunn <andrew@lunn.ch>
To:     Vladimir Oltean <olteanv@gmail.com>
Cc:     Florian Fainelli <f.fainelli@gmail.com>,
        netdev <netdev@vger.kernel.org>,
        Ioana Ciornei <ioana.ciornei@nxp.com>,
        Russell King <rmk+kernel@armlinux.org.uk>,
        Vivien Didelot <vivien.didelot@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH net-next] net: dsa: Deal with non-existing PHY/fixed-link
Message-ID: <20190610211133.GC2191@lunn.ch>
References: <20190610193150.22231-1-f.fainelli@gmail.com>
 <CA+h21hrcymxF7zk4yHFGhjxbLERTCU6WkfzLGQVoZ5Yxoo4xxw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CA+h21hrcymxF7zk4yHFGhjxbLERTCU6WkfzLGQVoZ5Yxoo4xxw@mail.gmail.com>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

> Hi Florian,
> 
> Can you give an example of when this is a valid use case, and why
> fixed-link is not appropriate?

A DSA link is used to connect two switches together. ZII devel b and c
are two boards which does this. Such links have the MACs connected
back to back, no PHYs involved. You can also connect a SoC interface
to the CPU port of a switch without having PHYs involved.

We have defined that CPU and DSA ports are always configured by the
driver to there maximum speed. Because of this, you often don't need a
fixed-link on CPU or DSA ports. So you will see most DT blobs don't
have any sort of PHY for the CPU or DSA ports.

You only need fixed-link when you need to slow a port down, e.g. a SoC
FE port connected to a switch 1G port.

    Andrew