Subject: Re: Q: fixed link

From: Andrew Lunn <[email-masked]>
Date: Sun, 8 Sep 2019 11:05:51 +0200

On Sun, Sep 08, 2019 at 10:30:51AM +0300, Ranran wrote:
> Hello,
> 
> In documentation of fixed-link it is said:"
> Some Ethernet MACs have a "fixed link", and are not connected to a
> normal MDIO-managed PHY device. For those situations, a Device Tree
> binding allows to describe a "fixed link".
> "
> Does it mean, that on using unmanaged switch ("no cpu" mode), it is
> better be used with fixed-link ?

Hi Ranran

Is there a MAC to MAC connection, or PHY to PHY connection?

If the interface MAC is directly connected to the switch MAC, fixed
link is what you should use. The fixed link will then tell the
interface MAC what speed it should use.

If you have back to back PHYs, you need a PHY driver for the PHY
connected to the interface MAC, to configure its speed, duplex
etc. The dumb switch should be controlling its PHY, and auto-neg will
probably work.

	 Andrew