net: phy: micrel: add cable test support for KSZ9477-class PHYs

Enable cable test support for KSZ9477-class PHYs by reusing the
existing KSZ9131 implementation.

This also adds support for 100Mbit-only PHYs like KSZ8563, which are
identified as KSZ9477. For these PHYs, only two wire pairs (A and B)
are active, so the cable test logic limits the pair_mask accordingly.

Support for KSZ8563 is untested but added based on its register
compatibility and PHY ID match.

Tested on KSZ9893 (Gigabit): open and short conditions were correctly
detected on all four pairs. Fault length reporting is functional and
varies by pair. For example:
- 2m cable: open faults reported ~1.2m (pairs B–D), 0.0m (pair A)
- No cable: all pairs report 0.0m fault length

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250610091354.4060454-4-o.rempel@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 13 insertions, 2 deletions

diff --git a/drivers/net/phy/micrel.c b/drivers/net/phy/micrel.c
index 68d86383e6c7..d0429dc8f561 100644
--- a/drivers/net/phy/micrel.c
+++ b/drivers/net/phy/micrel.c
@@ -1723,7 +1723,8 @@ static int ksz9x31_cable_test_fault_length(struct phy_device *phydev, u16 stat)
 	 *
 	 * distance to fault = (VCT_DATA - 22) * 4 / cable propagation velocity
 	 */
-	if (phydev_id_compare(phydev, PHY_ID_KSZ9131))
+	if (phydev_id_compare(phydev, PHY_ID_KSZ9131) ||
+	    phydev_id_compare(phydev, PHY_ID_KSZ9477))
 		dt = clamp(dt - 22, 0, 255);
 
 	return (dt * 400) / 10;
@@ -1797,12 +1798,20 @@ static int ksz9x31_cable_test_get_status(struct phy_device *phydev,
 					 bool *finished)
 {
 	struct kszphy_priv *priv = phydev->priv;
-	unsigned long pair_mask = 0xf;
+	unsigned long pair_mask;
 	int retries = 20;
 	int pair, ret, rv;
 
 	*finished = false;
 
+	if (linkmode_test_bit(ETHTOOL_LINK_MODE_1000baseT_Full_BIT,
+			      phydev->supported) ||
+	    linkmode_test_bit(ETHTOOL_LINK_MODE_1000baseT_Half_BIT,
+			      phydev->supported))
+		pair_mask = 0xf; /* All pairs */
+	else
+		pair_mask = 0x3; /* Pairs A and B only */
+
 	/* Try harder if link partner is active */
 	while (pair_mask && retries--) {
 		for_each_set_bit(pair, &pair_mask, 4) {
@@ -5790,6 +5799,8 @@ static struct phy_driver ksphy_driver[] = {
 	.resume		= ksz9477_resume,
 	.get_phy_stats	= kszphy_get_phy_stats,
 	.update_stats	= kszphy_update_stats,
+	.cable_test_start	= ksz9x31_cable_test_start,
+	.cable_test_get_status	= ksz9x31_cable_test_get_status,
 } };
 
 module_phy_driver(ksphy_driver);