linux-kernel - Re: [PATCH net-next] net: phy: micrel: Add support for lan8842

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Message-ID: <20250724062505.bl6mme4j3iuvvut7@DEN-DL-M31836.microchip.com>
Date: Thu, 24 Jul 2025 08:25:05 +0200
From: Horatiu Vultur <horatiu.vultur@...rochip.com>
To: Andrew Lunn <andrew@...n.ch>
CC: Oleksij Rempel <o.rempel@...gutronix.de>, <hkallweit1@...il.com>,
	<linux@...linux.org.uk>, <davem@...emloft.net>, <edumazet@...gle.com>,
	<kuba@...nel.org>, <pabeni@...hat.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: phy: micrel: Add support for lan8842

The 07/23/2025 16:28, Andrew Lunn wrote:

Hi,

> 
> > # FLF Behavior (Immediate Failure)
> > An FLF-enabled PHY is designed to report link instability almost
> > immediately (~1 ms). Instead of trying to recover silently, it
> > immediately reports a hard link failure to the operating system.
> >
> > # The Disadvantage in a Single-Link System
> >
> > For a system with only one link, this "fail-fast" approach can be a
> > disadvantage. Consider a short, recoverable noise burst:
> >
> > - Without FLF: The PHY uses its 750 ms grace period to recover. The
> > link stays up, and the service interruption is limited to brief packet
> > loss.
> >
> > - With FLF: The PHY reports "link down" after ~1 ms. The operating
> > system tears down the network interface. Even if the hardware recovers
> > quickly, the OS has to bring the interface back up, re-run DHCP, and
> > re-establish all application connections. This system-level recovery
> > often takes much longer than the original glitch.
> >
> > In short, FLF can turn a minor, recoverable physical-layer glitch into a
> > more disruptive, longer-lasting outage at the application level when
> > there is no backup link to switch to.
> 
> Fast link down can be a useful feature to have, but the PHY should
> default to what 802.3 says. There is however:
> 
> ETHTOOL_PHY_FAST_LINK_DOWN
> 
> which two drivers support.

OK, by default the FLF support will not be enabled and then in a
different patch I will allow to configure the FLF using
ETHTOOL_PHY_FAST_LINK_DOWN.


> 
>         Andrew

-- 
/Horatiu