linux-kernel - Re: [PATCH net v1 2/2] net: phy: microchip: lan87xx: do not report SQI if no link

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Message-ID: <47b227f0-d445-47ba-9386-e8b77b733c26@lunn.ch>
Date: Wed, 3 Jul 2024 20:57:51 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Woojung Huh <woojung.huh@...rochip.com>,
	Arun Ramadoss <arun.ramadoss@...rochip.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Yuiko Oshino <yuiko.oshino@...rochip.com>, kernel@...gutronix.de,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH net v1 2/2] net: phy: microchip: lan87xx: do not report
 SQI if no link

On Wed, Jul 03, 2024 at 03:28:01PM +0200, Oleksij Rempel wrote:
> Do not report SQI if no link is detected. Otherwise ethtool will show
> non zero value even if no cable is attached.
> 
> Fixes: b649695248b15 ("net: phy: LAN87xx: add ethtool SQI support")
> Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> ---
>  drivers/net/phy/microchip_t1.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/net/phy/microchip_t1.c b/drivers/net/phy/microchip_t1.c
> index a35528497a576..22530a5b76365 100644
> --- a/drivers/net/phy/microchip_t1.c
> +++ b/drivers/net/phy/microchip_t1.c
> @@ -840,6 +840,9 @@ static int lan87xx_get_sqi(struct phy_device *phydev)
>  	u8 sqi_value = 0;
>  	int rc;
>  
> +	if (!phydev->link)
> +		return 0;
> +

Is this the correct place to fix this? Can any PHY report an SQI value
if there is no link? Maybe an automotive PHY using T1 and good old
fashioned CSMA/CD could report about background noise? But do they?

Maybe this should be fixed in linkstate_get_sqi()?

Also, maybe it should return -ENETDOWN, not 0. Do we want to say
"worse than class A SQI (unstable link)" when in fact the link is
"class G SQI (very good link)" once it is up?

	Andrew