netdev - Re: [PATCH v2 2/6] leds: trigger: Create a new LED netdev trigger for collision

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Date: Tue, 27 Feb 2024 17:03:14 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Bastien Curutchet <bastien.curutchet@...tlin.com>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>, Pavel Machek <pavel@....cz>,
	Lee Jones <lee@...nel.org>,
	Richard Cochran <richardcochran@...il.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, devicetree@...r.kernel.org,
	linux-leds@...r.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	herve.codina@...tlin.com, maxime.chevallier@...tlin.com,
	christophercordahi@...ometrics.ca
Subject: Re: [PATCH v2 2/6] leds: trigger: Create a new LED netdev trigger
 for collision

On Tue, Feb 27, 2024 at 10:39:41AM +0100, Bastien Curutchet wrote:
> Collisions on link does not fit into one of the existing netdev triggers.
> 
> Add TRIGGER_NETDEV_COLLISION in the enum led_trigger_netdev_modes.
> Add its definition in Documentation.
> Add its handling in ledtrig-netdev, it can only be supported by hardware
> so no software fallback is implemented.

How useful is collision? How did you test this? How did you cause
collisions to see if the LED actually worked?

As far as i can see, this is just a normal 100Base-T PHY. Everybody
uses that point-to-point nowadays. If it was an 100Base-T1, with a
shared medium, good old CSMA/CD then collision might actually be
useful.

I also disagree with not having software fallback:

ip -s link show eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
    link/ether 80:ee:73:83:60:27 brd ff:ff:ff:ff:ff:ff
    RX:     bytes    packets errors dropped  missed   mcast           
    4382213540983 2947876747      0       0       0  154890 
    TX:     bytes    packets errors dropped carrier collsns           
      18742773651  197507119      0       0       0       0

collsns = 0. The information is there in a standard format. However,
when did you last see it not 0?

	Andrew