net: phy: phy-c45: add SQI and SQI+ support for OATC14 10Base-T1S PHYs

Add support for reading Signal Quality Indicator (SQI) and enhanced SQI+
from OATC14 10Base-T1S PHYs.

- Introduce MDIO register definitions for DCQ_SQI and DCQ_SQIPLUS.
- Add `genphy_c45_oatc14_get_sqi_max()` to return the maximum supported
SQI/SQI+ level.
- Add `genphy_c45_oatc14_get_sqi()` to return the current SQI or SQI+
value.
- Update `include/linux/phy.h` to expose the new APIs.

SQI+ capability is read from the Advanced Diagnostic Features Capability
register (ADFCAP). If SQI+ is supported, the driver calculates the value
from the MSBs of the DCQ_SQIPLUS register; otherwise, it falls back to
basic SQI (0-7 levels). This enables ethtool to report the SQI value for
OATC14 10Base-T1S PHYs.

Open Alliance TC14 10BASE-T1S Advanced Diagnostic PHY Features
Specification ref:
https://opensig.org/wp-content/uploads/2025/06/OPEN_Alliance_10BASE-T1S_Advanced_PHY_features_for-automotive_Ethernet_V2.1b.pdf

Signed-off-by: Parthiban Veerasooran <[e-mail]>
Reviewed-by: Andrew Lunn <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/phy/mdio-open-alliance.h

···
 /* Advanced Diagnostic Features Capability Register*/
 #define MDIO_OATC14_ADFCAP		0xcc00
 #define OATC14_ADFCAP_HDD_CAPABILITY	GENMASK(10, 8)
+#define OATC14_ADFCAP_SQIPLUS_CAPABILITY	GENMASK(4, 1)
+#define OATC14_ADFCAP_SQI_CAPABILITY	BIT(0)
 
 /* Harness Defect Detection Register */
 #define MDIO_OATC14_HDD			0xcc01
···
 #define OATC14_HDD_START_CONTROL	BIT(13)
 #define OATC14_HDD_VALID		BIT(2)
 #define OATC14_HDD_SHORT_OPEN_STATUS	GENMASK(1, 0)
+
+/* Dynamic Channel Quality SQI Register */
+#define MDIO_OATC14_DCQ_SQI		0xcc03
+#define OATC14_DCQ_SQI_VALUE		GENMASK(2, 0)
+
+/* Dynamic Channel Quality SQI Plus Register */
+#define MDIO_OATC14_DCQ_SQIPLUS		0xcc04
+#define OATC14_DCQ_SQIPLUS_VALUE	GENMASK(7, 0)
+
+/* SQI is supported using 3 bits means 8 levels (0-7) */
+#define OATC14_SQI_MAX_LEVEL		7
 
 /* Bus Short/Open Status:
  * 0 0 - no fault; everything is ok. (Default)

drivers/net/phy/phy-c45.c

···
 				OATC14_HDD_START_CONTROL);
 }
 EXPORT_SYMBOL(genphy_c45_oatc14_cable_test_start);
+
+/**
+ * oatc14_update_sqi_capability - Read and update OATC14 10Base-T1S PHY SQI/SQI+
+ *                                capability
+ * @phydev: Pointer to the PHY device structure
+ *
+ * This helper reads the OATC14 ADFCAP capability register to determine whether
+ * the PHY supports SQI or SQI+ reporting.
+ *
+ * SQI+ capability is detected first. The SQI+ field indicates the number of
+ * valid MSBs (3–8), corresponding to 8–256 SQI+ levels. When present, the
+ * function stores the number of SQI+ bits and computes the maximum SQI+ value
+ * as (2^bits - 1).
+ *
+ * If SQI+ is not supported, the function checks for basic SQI capability,
+ * which provides 0–7 SQI levels.
+ *
+ * On success, the capability information is stored in
+ * @phydev->oatc14_sqi_capability and marked as updated.
+ *
+ * Return:
+ * * 0        - capability successfully read and stored
+ * * -EOPNOTSUPP - SQI/SQI+ not supported by this PHY
+ * * Negative errno on read failure
+ */
+static int oatc14_update_sqi_capability(struct phy_device *phydev)
+{
+	u8 bits;
+	int ret;
+
+	ret = phy_read_mmd(phydev, MDIO_MMD_VEND2, MDIO_OATC14_ADFCAP);
+	if (ret < 0)
+		return ret;
+
+	/* Check for SQI+ capability
+	 * 0 - SQI+ is not supported
+	 * (3-8) bits for (8-256) SQI+ levels supported
+	 */
+	bits = FIELD_GET(OATC14_ADFCAP_SQIPLUS_CAPABILITY, ret);
+	if (bits) {
+		phydev->oatc14_sqi_capability.sqiplus_bits = bits;
+		/* Max sqi+ level supported: (2 ^ bits) - 1 */
+		phydev->oatc14_sqi_capability.sqi_max = BIT(bits) - 1;
+		goto update_done;
+	}
+
+	/* Check for SQI capability
+	 * 0 - SQI is not supported
+	 * 1 - SQI is supported (0-7 levels)
+	 */
+	if (ret & OATC14_ADFCAP_SQI_CAPABILITY) {
+		phydev->oatc14_sqi_capability.sqi_max = OATC14_SQI_MAX_LEVEL;
+		goto update_done;
+	}
+
+	return -EOPNOTSUPP;
+
+update_done:
+	phydev->oatc14_sqi_capability.updated = true;
+	return 0;
+}
+
+/**
+ * genphy_c45_oatc14_get_sqi_max - Get maximum supported SQI or SQI+ level of
+ *				   OATC14 10Base-T1S PHY
+ * @phydev: pointer to the PHY device structure
+ *
+ * This function returns the maximum supported Signal Quality Indicator (SQI) or
+ * SQI+ level. The SQI capability is updated on first invocation if it has not
+ * already been updated.
+ *
+ * Return:
+ * * Maximum SQI/SQI+ level supported
+ * * Negative errno on capability read failure
+ */
+int genphy_c45_oatc14_get_sqi_max(struct phy_device *phydev)
+{
+	int ret;
+
+	if (!phydev->oatc14_sqi_capability.updated) {
+		ret = oatc14_update_sqi_capability(phydev);
+		if (ret)
+			return ret;
+	}
+
+	return phydev->oatc14_sqi_capability.sqi_max;
+}
+EXPORT_SYMBOL(genphy_c45_oatc14_get_sqi_max);
+
+/**
+ * genphy_c45_oatc14_get_sqi - Get Signal Quality Indicator (SQI) from an OATC14
+ *			       10Base-T1S PHY
+ * @phydev: pointer to the PHY device structure
+ *
+ * This function reads the SQI+ or SQI value from an OATC14-compatible
+ * 10Base-T1S PHY. If SQI+ capability is supported, the function returns the
+ * extended SQI+ value; otherwise, it returns the basic SQI value. The SQI
+ * capability is updated on first invocation if it has not already been updated.
+ *
+ * Return:
+ * * SQI/SQI+ value on success
+ * * Negative errno on read failure
+ */
+int genphy_c45_oatc14_get_sqi(struct phy_device *phydev)
+{
+	u8 shift;
+	int ret;
+
+	if (!phydev->oatc14_sqi_capability.updated) {
+		ret = oatc14_update_sqi_capability(phydev);
+		if (ret)
+			return ret;
+	}
+
+	/* Calculate and return SQI+ value if supported */
+	if (phydev->oatc14_sqi_capability.sqiplus_bits) {
+		ret = phy_read_mmd(phydev, MDIO_MMD_VEND2,
+				   MDIO_OATC14_DCQ_SQIPLUS);
+		if (ret < 0)
+			return ret;
+
+		/* SQI+ uses N MSBs out of 8 bits, left-aligned with padding 1's
+		 * Calculate the right-shift needed to isolate the N bits.
+		 */
+		shift = 8 - phydev->oatc14_sqi_capability.sqiplus_bits;
+
+		return (ret & OATC14_DCQ_SQIPLUS_VALUE) >> shift;
+	}
+
+	/* Read and return SQI value if SQI+ capability is not supported */
+	ret = phy_read_mmd(phydev, MDIO_MMD_VEND2, MDIO_OATC14_DCQ_SQI);
+	if (ret < 0)
+		return ret;
+
+	return ret & OATC14_DCQ_SQI_VALUE;
+}
+EXPORT_SYMBOL(genphy_c45_oatc14_get_sqi);

include/linux/phy.h

···
 struct macsec_ops;
 
 /**
+ * struct phy_oatc14_sqi_capability - SQI capability information for OATC14
+ *                                    10Base-T1S PHY
+ * @updated: Indicates whether the SQI capability fields have been updated.
+ * @sqi_max: Maximum supported Signal Quality Indicator (SQI) level reported by
+ *           the PHY.
+ * @sqiplus_bits: Bits for SQI+ levels supported by the PHY.
+ *                0 - SQI+ is not supported
+ *                3 - SQI+ is supported, using 3 bits (8 levels)
+ *                4 - SQI+ is supported, using 4 bits (16 levels)
+ *                5 - SQI+ is supported, using 5 bits (32 levels)
+ *                6 - SQI+ is supported, using 6 bits (64 levels)
+ *                7 - SQI+ is supported, using 7 bits (128 levels)
+ *                8 - SQI+ is supported, using 8 bits (256 levels)
+ *
+ * This structure is used by the OATC14 10Base-T1S PHY driver to store the SQI
+ * and SQI+ capability information retrieved from the PHY.
+ */
+struct phy_oatc14_sqi_capability {
+	bool updated;
+	int sqi_max;
+	u8 sqiplus_bits;
+};
+
+/**
  * struct phy_device - An instance of a PHY
  *
  * @mdio: MDIO bus this PHY is on
···
  * @link_down_events: Number of times link was lost
  * @shared: Pointer to private data shared by phys in one package
  * @priv: Pointer to driver private data
+ * @oatc14_sqi_capability: SQI capability information for OATC14 10Base-T1S PHY
  *
  * interrupts currently only supports enabled or disabled,
  * but could be changed in the future to support enabling
···
 	/* MACsec management functions */
 	const struct macsec_ops *macsec_ops;
 #endif
+
+	struct phy_oatc14_sqi_capability oatc14_sqi_capability;
 };
 
 /* Generic phy_device::dev_flags */
···
 int genphy_c45_oatc14_cable_test_start(struct phy_device *phydev);
 int genphy_c45_oatc14_cable_test_get_status(struct phy_device *phydev,
 					    bool *finished);
+int genphy_c45_oatc14_get_sqi_max(struct phy_device *phydev);
+int genphy_c45_oatc14_get_sqi(struct phy_device *phydev);
 
 /* The gen10g_* functions are the old Clause 45 stub */
 int gen10g_config_aneg(struct phy_device *phydev);