netdev - Re: Ethtool query: Reset advertised speed modes if speed value is not passed in "set_link

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Message-ID: <20240308141624.sj3m7imkcaeq2vjy@lion.mk-sys.cz>
Date: Fri, 8 Mar 2024 15:16:24 +0100
From: Michal Kubecek <mkubecek@...e.cz>
To: Andrew Lunn <andrew@...n.ch>
Cc: "Sagar Dhoot (QUIC)" <quic_sdhoot@...cinc.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Nagarjuna Chaganti (QUIC)" <quic_nchagant@...cinc.com>,
	"Priya Tripathi (QUIC)" <quic_ppriyatr@...cinc.com>
Subject: Re: Ethtool query: Reset advertised speed modes if speed value is
 not passed in "set_link_ksettings"

On Fri, Mar 08, 2024 at 02:56:30PM +0100, Andrew Lunn wrote:
> On Fri, Mar 08, 2024 at 06:33:00AM +0000, Sagar Dhoot (QUIC) wrote:
> > Hi Andrew,
> > 
> > Thanks for the quick response. Maybe I have put up a confusing scenario.
> > 
> > Let me rephrase with autoneg on.
> > 
> > 1. "ethtool eth_interface"
> > 2. "ethtool -s eth_interface speed 25000 autoneg on"
> 
> phylib will ignore speed if autoneg is on

It is not passed there. With "autoneg on", speed, duplex and lanes are
interpreted as conditions for modes to be advertised, i.e. they are
translated to the same request as "advertise ..." with list of supported
modes matching the parameters that were used.

In the ioctl code path, this logic is handled in userspace ethtool (but
only in a limited scope), for netlink API the logic is implemented in
kernel function ethnl_auto_linkmodes() in net/ethtool/linkmodes.c.

Michal

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