linux-kernel - Re: Query regarding Phy loopback support

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Message-ID: <aNA5l3JEl5JMHfZM@test-OptiPlex-Tower-Plus-7010>
Date: Sun, 21 Sep 2025 23:14:55 +0530
From: Hariprasad Kelam <hkelam@...vell.com>
To: Andrew Lunn <andrew@...n.ch>
CC: <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kuba@...nel.org>, <davem@...emloft.net>, <sgoutham@...vell.com>,
        <gakula@...vell.com>, <sbhatta@...vell.com>, <naveenm@...vell.com>,
        <edumazet@...gle.com>, <pabeni@...hat.com>, <andrew+netdev@...n.ch>,
        <bbhushan2@...vell.com>
Subject: Re: Query regarding Phy loopback support

On 2025-09-16 at 22:13:20, Andrew Lunn (andrew@...n.ch) wrote:
> On Tue, Sep 16, 2025 at 04:48:56PM +0530, Hariprasad Kelam wrote:
> > We're looking for a standard way to configure PHY loopback on a network 
> > interface using common Linux tools like ethtool, ip, or devlink.
> > 
> > Currently, ethtool -k eth0 loopback on enables a generic loopback, but it 
> > doesn't specify if it's an internal, external, or PHY loopback. 
> > Need suggestions to implement this feature in a standard way.
> 
> What actually do you mean by PHY loopback?

The Octeon silicon series supports both MAC (RPM) and PHY (GSERM) loopback 
modes for testing.

We are seeking a solution to support the following loopback types:

MAC Level

Far-end loopback: Ingress data is routed back to egress data (MAC-to-MAC).

Near-end external loopback: Egress traffic is routed back to ingress traffic at the PCS layer.

PHY Level

Near-end digital loopback

Near-end analog loopback

Far-end digital loopback

Far-end analog loopback

We need suggestions on how to enable and manage these specific modes.

Thanks,
Hariprasad k