Merge branch 'net-phy-dp83822-add-support-for-changing-the-mac-series-termination'

Dimitri Fedrau says:

====================
net: phy: dp83822: Add support for changing the MAC series termination

The dp83822 provides the possibility to set the resistance value of the
the MAC series termination. Modifying the resistance to an appropriate
value can reduce signal reflections and therefore improve signal quality.

v2: https://lore.kernel.org/20250408-dp83822-mac-impedance-v2-0-fefeba4a9804@liebherr.com
v1: https://lore.kernel.org/20250307-dp83822-mac-impedance-v1-0-bdd85a759b45@liebherr.com
====================

Link: https://patch.msgid.link/20250416-dp83822-mac-impedance-v3-0-028ac426cddb@liebherr.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

5 files changed, 65 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/net/ethernet-phy.yaml b/Documentation/devicetree/bindings/net/ethernet-phy.yaml
index 824bbe4333b7..71e2cd32580f 100644
--- a/Documentation/devicetree/bindings/net/ethernet-phy.yaml
+++ b/Documentation/devicetree/bindings/net/ethernet-phy.yaml
@@ -238,6 +238,16 @@ properties:
       peak-to-peak specified in ANSI X3.263. When omitted, the PHYs default
       will be left as is.
 
+  mac-termination-ohms:
+    maximum: 200
+    description:
+      The xMII signals need series termination on the driver side to match both
+      the output driver impedance and the line characteristic impedance, to
+      prevent reflections and EMI problems. Select a resistance value which is
+      supported by the builtin resistors of the PHY, otherwise the resistors may
+      have to be placed on board. When omitted, the PHYs default will be left as
+      is.
+
   leds:
     type: object
 
diff --git a/Documentation/devicetree/bindings/net/ti,dp83822.yaml b/Documentation/devicetree/bindings/net/ti,dp83822.yaml
index 50c24248df26..28a0bddb9af9 100644
--- a/Documentation/devicetree/bindings/net/ti,dp83822.yaml
+++ b/Documentation/devicetree/bindings/net/ti,dp83822.yaml
@@ -122,6 +122,9 @@ properties:
       - free-running
       - recovered
 
+  mac-termination-ohms:
+    enum: [43, 44, 46, 48, 50, 53, 55, 58, 61, 65, 69, 73, 78, 84, 91, 99]
+
 required:
   - reg
 
@@ -137,6 +140,7 @@ examples:
         rx-internal-delay-ps = <1>;
         tx-internal-delay-ps = <1>;
         ti,gpio2-clk-out = "xi";
+        mac-termination-ohms = <43>;
       };
     };
 
diff --git a/drivers/net/phy/dp83822.c b/drivers/net/phy/dp83822.c
index 14f361549638..490c9f4e5d4e 100644
--- a/drivers/net/phy/dp83822.c
+++ b/drivers/net/phy/dp83822.c
@@ -33,6 +33,7 @@
 #define MII_DP83822_MLEDCR	0x25
 #define MII_DP83822_LDCTRL	0x403
 #define MII_DP83822_LEDCFG1	0x460
+#define MII_DP83822_IOCTRL	0x461
 #define MII_DP83822_IOCTRL1	0x462
 #define MII_DP83822_IOCTRL2	0x463
 #define MII_DP83822_GENCFG	0x465
@@ -118,6 +119,9 @@
 #define DP83822_LEDCFG1_LED1_CTRL	GENMASK(11, 8)
 #define DP83822_LEDCFG1_LED3_CTRL	GENMASK(7, 4)
 
+/* IOCTRL bits */
+#define DP83822_IOCTRL_MAC_IMPEDANCE_CTRL	GENMASK(4, 1)
+
 /* IOCTRL1 bits */
 #define DP83822_IOCTRL1_GPIO3_CTRL		GENMASK(10, 8)
 #define DP83822_IOCTRL1_GPIO3_CTRL_LED3		BIT(0)
@@ -202,6 +206,7 @@ struct dp83822_private {
 	u32 gpio2_clk_out;
 	bool led_pin_enable[DP83822_MAX_LED_PINS];
 	int tx_amplitude_100base_tx_index;
+	int mac_termination_index;
 };
 
 static int dp83822_config_wol(struct phy_device *phydev,
@@ -533,6 +538,12 @@ static int dp83822_config_init(struct phy_device *phydev)
 			       FIELD_PREP(DP83822_100BASE_TX_LINE_DRIVER_SWING,
 					  dp83822->tx_amplitude_100base_tx_index));
 
+	if (dp83822->mac_termination_index >= 0)
+		phy_modify_mmd(phydev, MDIO_MMD_VEND2, MII_DP83822_IOCTRL,
+			       DP83822_IOCTRL_MAC_IMPEDANCE_CTRL,
+			       FIELD_PREP(DP83822_IOCTRL_MAC_IMPEDANCE_CTRL,
+					  dp83822->mac_termination_index));
+
 	err = dp83822_config_init_leds(phydev);
 	if (err)
 		return err;
@@ -736,6 +747,10 @@ static const u32 tx_amplitude_100base_tx_gain[] = {
 	93, 95, 97, 98, 100, 102, 103, 105,
 };
 
+static const u32 mac_termination[] = {
+	99, 91, 84, 78, 73, 69, 65, 61, 58, 55, 53, 50, 48, 46, 44, 43,
+};
+
 static int dp83822_of_init_leds(struct phy_device *phydev)
 {
 	struct device_node *node = phydev->mdio.dev.of_node;
@@ -852,6 +867,23 @@ static int dp83822_of_init(struct phy_device *phydev)
 		}
 	}
 
+	ret = phy_get_mac_termination(phydev, dev, &val);
+	if (!ret) {
+		for (i = 0; i < ARRAY_SIZE(mac_termination); i++) {
+			if (mac_termination[i] == val) {
+				dp83822->mac_termination_index = i;
+				break;
+			}
+		}
+
+		if (dp83822->mac_termination_index < 0) {
+			phydev_err(phydev,
+				   "Invalid value for mac-termination-ohms property (%u)\n",
+				   val);
+			return -EINVAL;
+		}
+	}
+
 	return dp83822_of_init_leds(phydev);
 }
 
@@ -931,6 +963,7 @@ static int dp8382x_probe(struct phy_device *phydev)
 		return -ENOMEM;
 
 	dp83822->tx_amplitude_100base_tx_index = -1;
+	dp83822->mac_termination_index = -1;
 	phydev->priv = dp83822;
 
 	return 0;
diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index cc6c209fe702..f85c172c446c 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -2975,6 +2975,21 @@ int phy_get_tx_amplitude_gain(struct phy_device *phydev, struct device *dev,
 }
 EXPORT_SYMBOL_GPL(phy_get_tx_amplitude_gain);
 
+/**
+ * phy_get_mac_termination - stores MAC termination in @val
+ * @phydev: phy_device struct
+ * @dev: pointer to the devices device struct
+ * @val: MAC termination
+ *
+ * Returns: 0 on success, < 0 on failure
+ */
+int phy_get_mac_termination(struct phy_device *phydev, struct device *dev,
+			    u32 *val)
+{
+	return phy_get_u32_property(dev, "mac-termination-ohms", val);
+}
+EXPORT_SYMBOL_GPL(phy_get_mac_termination);
+
 static int phy_led_set_brightness(struct led_classdev *led_cdev,
 				  enum led_brightness value)
 {
diff --git a/include/linux/phy.h b/include/linux/phy.h
index fb755358d965..066a28a4b64b 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h
@@ -2040,6 +2040,9 @@ int phy_get_tx_amplitude_gain(struct phy_device *phydev, struct device *dev,
 			      enum ethtool_link_mode_bit_indices linkmode,
 			      u32 *val);
 
+int phy_get_mac_termination(struct phy_device *phydev, struct device *dev,
+			    u32 *val);
+
 void phy_resolve_pause(unsigned long *local_adv, unsigned long *partner_adv,
 		       bool *tx_pause, bool *rx_pause);