linux-kernel - Re: [PATCH] net: phy: phy_ethtool_ksettings

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Message-ID: <20241202105934.0eddb032@fedora.home>
Date: Mon, 2 Dec 2024 10:59:34 +0100
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: Nikita Yushchenko <nikita.yoush@...entembedded.com>
Cc: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>,
 Russell King <linux@...linux.org.uk>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
 <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, Michael Dege <michael.dege@...esas.com>,
 Christian Mardmoeller <christian.mardmoeller@...esas.com>, Dennis Ostermann
 <dennis.ostermann@...esas.com>
Subject: Re: [PATCH] net: phy: phy_ethtool_ksettings_set: Allow any
 supported speed

Hello Nikita,

On Mon, 2 Dec 2024 14:20:17 +0500
Nikita Yushchenko <nikita.yoush@...entembedded.com> wrote:

> Hello.
> 
> > What's your use-case to need >1G fixed-settings link ?  
> 
> My hardware is Renesas VC4 board (based on Renesas S4 SoC), network driver is rswitch, PHY in question 
> is Marvell 88Q3344 (2.5G Base-T1).

Ok so it's baseT1, which is indeed different than the BaseT4 case I was
mentionning. It could be good to include that in the commit log :)

> To get two such PHYs talk to each other, one of the two has to be manually configured as slave.
> (e.g. ethtool -s tsn0 master-slave forced-slave).
> 
> This gets handled via driver's ethtool set_link_ksettings method, which is currently set to
> phy_ethtool_ksettings_set().
> 
> Writing a custom set_link_ksettings method just to not error out when speed is 2500 looks ugly.

Yes and this would apply to any PHY that does >1G BaseT1. The thing is,
while it does solve the problem you're facing, the current proposition
will impact 2.5G/5G/10GBaseT4.

I don't think you need to write a custom set_link_ksettings, however we
should make an exception for BaseT1. Maybe add an extra condition in 
phy_ethtool_ksettings_set() to check in the advertising/supported if we
are dealing with a BaseT1 PHY, and if so bypass the check for
10/100/1000 speeds, as it doesn't apply in your case ? 

Maybe the PHY maintainers have better ideas though.

Thanks,

Maxime