On Wed, Aug 20, 2025 at 05:03:14AM +0200, Andrew Lunn wrote:

quoted

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.

In the case of the cable test, MDI-X does not affect the reported
results, or if it does, we can actively change the configuration and
re-run the test. For SQI/MSE on this chip, however, the measurement is
purely passive. If the hardware does not expose an MDI-X indicator, we
cannot reliably assign the values to a specific pair, so we need the
LINK selector to avoid returning misleading data.

quoted

@@ -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? 

Good point. I'll remove this part of comment.

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