linux-kernel - Re: [PATCH net-next v2 1/5] ethtool: introduce core UAPI and driver API for PHY MSE diagnostics

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Message-ID: <489b2959-3374-4766-a982-9e7c26077899@lunn.ch>
Date: Wed, 20 Aug 2025 05:03:14 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: Jakub Kicinski <kuba@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Donald Hunter <donald.hunter@...il.com>,
	Jonathan Corbet <corbet@....net>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Kory Maincent <kory.maincent@...tlin.com>,
	Maxime Chevallier <maxime.chevallier@...tlin.com>,
	Nishanth Menon <nm@...com>, kernel@...gutronix.de,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	UNGLinuxDriver@...rochip.com, linux-doc@...r.kernel.org,
	Michal Kubecek <mkubecek@...e.cz>, Roan van Dijk <roan@...tonic.nl>
Subject: Re: [PATCH net-next v2 1/5] ethtool: introduce core UAPI and driver
 API for PHY MSE diagnostics

> Channel-to-pair mapping is normally straightforward, but in some cases
> (e.g. 100BASE-TX with MDI-X resolution unknown) the mapping is ambiguous.
> If hardware does not expose MDI-X status, the exact pair cannot be
> determined. To avoid returning misleading per-channel data in this case,
> a LINK selector is defined for aggregate MSE measurements.

This is the same with cable test. The API just labels the pairs using

        ETHTOOL_A_CABLE_PAIR_A,
        ETHTOOL_A_CABLE_PAIR_B,
        ETHTOOL_A_CABLE_PAIR_C,
        ETHTOOL_A_CABLE_PAIR_D,

It does not take into account MDI-X or anything.

> @@ -1174,6 +1246,60 @@ struct phy_driver {
>  	/** @get_sqi_max: Get the maximum signal quality indication */
>  	int (*get_sqi_max)(struct phy_device *dev);
>  
> +	/**
> +	 * get_mse_config - Get configuration and scale of MSE measurement
> +	 * @dev:    PHY device
> +	 * @config: Output (filled on success)
> +	 *
> +	 * Fill @config with the PHY's MSE configuration for the current
> +	 * link mode: scale limits (max_average_mse, max_peak_mse), update
> +	 * interval (refresh_rate_ps), sample length (num_symbols) and the
> +	 * capability bitmask (supported_caps).
> +	 *
> +	 * Implementations may defer configuration until hardware has
> +	 * converged; in that case they should return -EAGAIN and allow the
> +	 * caller to retry later.
> +	 *
> +	 * Return:
> +	 *  * 0              - success, @config is valid
> +	 *  * -EOPNOTSUPP    - MSE configuration not implemented by the PHY
> +	 *		       or not supported in the current link mode
> +	 *  * -ENETDOWN      - link is down and configuration is not
> +	 *		       available in that state

This seems a bit odd. phylib knows the state of the link. If it is
down, why would it even ask? 

	Andrew