netdev - Re: [PATCH net-next v2 2/2] net: phylib: do not disable autoneg for fixed speeds >= 1G

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Message-ID: <e8b4ae1d-de5b-4f6e-a94c-0e0e3a4bd643@lunn.ch>
Date: Sun, 11 Aug 2024 18:13:52 +0200
From: Andrew Lunn <andrew@...n.ch>
To: "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>
Cc: Heiner Kallweit <hkallweit1@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
	Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next v2 2/2] net: phylib: do not disable autoneg for
 fixed speeds >= 1G

On Thu, Aug 08, 2024 at 12:41:22PM +0100, Russell King (Oracle) wrote:
> We have an increasing number of drivers that are forcing
> auto-negotiation to be enabled for speeds of 1G or faster.
> 
> It would appear that auto-negotiation is mandatory for speeds above
> 100M. In 802.3, Annex 40C's state diagrams seems to imply that
> mr_autoneg_enable (BMCR AN ENABLE) doesn't affect whether or not the
> AN state machines work for 1000base-T, and some PHY datasheets (e.g.
> Marvell Alaska) state that disabling mr_autoneg_enable leaves AN
> enabled but forced to 1G full duplex.
> 
> Other PHY datasheets imply that BMCR AN ENABLE should not be cleared
> for >= 1G.
> 
> Thus, this should be handled in phylib rather than in each driver.
> 
> Rather than erroring out, arrange to implement the Marvell Alaska
> solution but in software for all PHYs: generate an appropriate
> single-speed advertisement for the requested speed, and keep AN
> enabled to the PHY driver. However, to avoid userspace API breakage,
> continue to report to userspace that we have AN disabled.
> 
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew