The ADIN1200/ADIN1300 provide a control bit that selects between normal
receive termination and the lowest common mode impedance for 100BASE-TX
operation. This behavior is controlled through the Low Power Termination
register (B_100_ZPTM_EN_DIMRX).

Bit 0 of this register enables normal termination when set (this is the
default), and selects the lowest common mode impedance when cleared.

Signed-off-by: Osose Itua <osose.itua@savoirfairelinux.com>
---
 drivers/net/phy/adin.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/drivers/net/phy/adin.c b/drivers/net/phy/adin.c
index 7fa713ca8d45..e8b778cb191d 100644
--- a/drivers/net/phy/adin.c
+++ b/drivers/net/phy/adin.c
@@ -4,6 +4,7 @@
  *
  * Copyright 2019 Analog Devices Inc.
  */
+#include <cerrno>
 #include <linux/kernel.h>
 #include <linux/bitfield.h>
 #include <linux/delay.h>
@@ -89,6 +90,9 @@
 #define ADIN1300_CLOCK_STOP_REG			0x9400
 #define ADIN1300_LPI_WAKE_ERR_CNT_REG		0xa000
 
+#define ADIN1300_B_100_ZPTM_DIMRX		0xB685
+#define ADIN1300_B_100_ZPTM_EN_DIMRX		BIT(0)
+
 #define ADIN1300_CDIAG_RUN			0xba1b
 #define   ADIN1300_CDIAG_RUN_EN			BIT(0)
 
@@ -522,6 +526,32 @@ static int adin_config_clk_out(struct phy_device *phydev)
 			      ADIN1300_GE_CLK_CFG_MASK, sel);
 }
 
+static int adin_config_zptm100(struct phy_device *phydev)
+{
+	struct device *dev = &phydev->mdio.dev;
+	int reg;
+	int rc;
+
+	if (!(device_property_read_bool(dev, "adi,low-cmode-impedance")))
+		return 0;
+
+	/* set to 0 to configure for lowest common-mode impedance */
+	rc = phy_write_mmd(phydev, MDIO_MMD_VEND1, ADIN1300_B_100_ZPTM_DIMRX, 0x0);
+	if (rc < 0)
+		return rc;
+
+	reg = phy_read_mmd(phydev, MDIO_MMD_VEND1, ADIN1300_B_100_ZPTM_DIMRX);
+	if (reg < 0)
+		return reg;
+
+	if (!(reg & ADIN1300_B_100_ZPTM_EN_DIMRX)) {
+		phydev_err(phydev, "Failed to set lowest common-mode impedance.\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int adin_config_init(struct phy_device *phydev)
 {
 	int rc;
@@ -548,6 +578,10 @@ static int adin_config_init(struct phy_device *phydev)
 	if (rc < 0)
 		return rc;
 
+	rc = adin_config_zptm100(phydev);
+	if (rc < 0)
+		return rc;
+
 	phydev_dbg(phydev, "PHY is using mode '%s'\n",
 		   phy_modes(phydev->interface));