From cbc38ebf8ff6d01cd11270d99762d4216ff4237d Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.org>
Date: Mon, 26 Nov 2018 19:46:58 +0000
Subject: [PATCH] net: lan78xx: Support auto-downshift to 100Mb/s

Ethernet cables with faulty or missing pairs (specifically pairs C and
D) allow auto-negotiation to 1000Mbs, but do not support the successful
establishment of a link. Add a DT property, "microchip,downshift-after",
to configure the number of auto-negotiation failures after which it
falls back to 100Mbs. Valid values are 2, 3, 4, 5 and 0, where 0 means
never downshift.

Signed-off-by: Phil Elwell <phil@raspberrypi.org>
---
 .../bindings/net/microchip,lan78xx.txt        |  3 +++
 drivers/net/phy/microchip.c                   | 27 +++++++++++++++++++
 include/linux/microchipphy.h                  |  8 ++++++
 3 files changed, 38 insertions(+)

--- a/Documentation/devicetree/bindings/net/microchip,lan78xx.txt
+++ b/Documentation/devicetree/bindings/net/microchip,lan78xx.txt
@@ -14,6 +14,9 @@ Optional properties of the embedded PHY:
 - microchip,led-modes: a 0..4 element vector, with each element configuring
   the operating mode of an LED. Omitted LEDs are turned off. Allowed values
   are defined in "include/dt-bindings/net/microchip-lan78xx.h".
+- microchip,downshift-after: sets the number of failed auto-negotiation
+  attempts after which the link is downgraded from 1000BASE-T. Should be one of
+  2, 3, 4, 5 or 0, where 0 means never downshift.
 
 Example:
 
--- a/drivers/net/phy/microchip.c
+++ b/drivers/net/phy/microchip.c
@@ -217,6 +217,7 @@ static int lan88xx_probe(struct phy_devi
 	struct device *dev = &phydev->mdio.dev;
 	struct lan88xx_priv *priv;
 	u32 led_modes[4];
+	u32 downshift_after = 0;
 	int len;
 
 	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
@@ -246,6 +247,32 @@ static int lan88xx_probe(struct phy_devi
 		return -EINVAL;
 	}
 
+	if (!of_property_read_u32(dev->of_node,
+				  "microchip,downshift-after",
+				  &downshift_after)) {
+		u32 mask = LAN78XX_PHY_CTRL3_DOWNSHIFT_CTRL_MASK;
+		u32 val= LAN78XX_PHY_CTRL3_AUTO_DOWNSHIFT;
+
+		switch (downshift_after) {
+		case 2:	val |= LAN78XX_PHY_CTRL3_DOWNSHIFT_CTRL_2;
+			break;
+		case 3:	val |= LAN78XX_PHY_CTRL3_DOWNSHIFT_CTRL_3;
+			break;
+		case 4:	val |= LAN78XX_PHY_CTRL3_DOWNSHIFT_CTRL_4;
+			break;
+		case 5:	val |= LAN78XX_PHY_CTRL3_DOWNSHIFT_CTRL_5;
+			break;
+		case 0: // Disable completely
+			mask = LAN78XX_PHY_CTRL3_AUTO_DOWNSHIFT;
+			val = 0;
+			break;
+		default:
+			return -EINVAL;
+		}
+		(void)phy_modify_paged(phydev, 1, LAN78XX_PHY_CTRL3,
+				       mask, val);
+	}
+
 	/* these values can be used to identify internal PHY */
 	priv->chip_id = phy_read_mmd(phydev, 3, LAN88XX_MMD3_CHIP_ID);
 	priv->chip_rev = phy_read_mmd(phydev, 3, LAN88XX_MMD3_CHIP_REV);
--- a/include/linux/microchipphy.h
+++ b/include/linux/microchipphy.h
@@ -61,6 +61,14 @@
 /* Registers specific to the LAN7800/LAN7850 embedded phy */
 #define LAN78XX_PHY_LED_MODE_SELECT		(0x1D)
 
+#define LAN78XX_PHY_CTRL3			(0x14)
+#define LAN78XX_PHY_CTRL3_AUTO_DOWNSHIFT	(0x0010)
+#define LAN78XX_PHY_CTRL3_DOWNSHIFT_CTRL_MASK	(0x000c)
+#define LAN78XX_PHY_CTRL3_DOWNSHIFT_CTRL_2	(0x0000)
+#define LAN78XX_PHY_CTRL3_DOWNSHIFT_CTRL_3	(0x0004)
+#define LAN78XX_PHY_CTRL3_DOWNSHIFT_CTRL_4	(0x0008)
+#define LAN78XX_PHY_CTRL3_DOWNSHIFT_CTRL_5	(0x000c)
+
 /* DSP registers */
 #define PHY_ARDENNES_MMD_DEV_3_PHY_CFG		(0x806A)
 #define PHY_ARDENNES_MMD_DEV_3_PHY_CFG_ZD_DLY_EN_	(0x2000)
