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

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Message-ID: <Zd4NJUcN3p/Vi2vn@shell.armlinux.org.uk>
Date: Tue, 27 Feb 2024 16:26:13 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>
Cc: Bastien Curutchet <bastien.curutchet@...tlin.com>,
	"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>,
	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 05:03:14PM +0100, Andrew Lunn wrote:
> 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.

That's largely irrelevant when it comes to collisions. If the link has
negotiated half-duplex mode (which we still support) then even on
twisted pair, there can be collisions, even though TX and RX are using
separate pairs. It's a quirk of 802.3 that this is the case.

-- 
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