linux-kernel - Re: [PATCH net-next] net: renesas: rswitch: cleanup max

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Message-ID: <af3fb019-48fa-42e0-9e02-a4b0d3a724bc@cogentembedded.com>
Date: Wed, 5 Feb 2025 17:26:09 +0100
From: Nikita Yushchenko <nikita.yoush@...entembedded.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Geert Uytterhoeven <geert+renesas@...der.be>, netdev@...r.kernel.org,
 linux-renesas-soc@...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-next] net: renesas: rswitch: cleanup max_speed setting

> You should only need max-speed when you have a PHY which can do more
> than the MAC.

This is exactly the case.

Unfortunately I don't have the spider schematics nearby, but AFAIU (one of flavours of) the board has 
PHYs capable of 5G but connected over SGMII.  When two such boards are connected to each other, on 
mainline kernel auto-negotiation takes noticeably longer than with the Renesas BSP kernel.

> Also, phylink handles this a lot better than phylib. So you might want
> to change rswitch to phylink, especially if you have link speeds > 1G.

The reverse switch happened in commit c16a5033f77b ("net: renesas: rswitch: Convert to phy_device").
I did not check the tech details of that, but decided not to touch it.

Nikita