net: phy: realtek: read actual speed to detect downshift

At least some integrated PHY's in RTL8168/RTL8125 chip versions support
downshift, and the actual link speed can be read from a vendor-specific
register. Info about this register was provided by Realtek.
More details about downshift configuration (e.g. number of attempts)
aren't available, therefore the downshift tunable is not implemented.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/realtek.c

@@ -49,6 +49,8 @@
 #define RTL_LPADV_5000FULL			BIT(6)
 #define RTL_LPADV_2500FULL			BIT(5)
 
+#define RTLGEN_SPEED_MASK			0x0630
+
 #define RTL_GENERIC_PHYID			0x001cc800
 
 MODULE_DESCRIPTION("Realtek PHY driver");
@@ -309,6 +311,55 @@ static int rtl8366rb_config_init(struct phy_device *phydev)
 	return ret;
 }
 
+/* get actual speed to cover the downshift case */
+static int rtlgen_get_speed(struct phy_device *phydev)
+{
+	int val;
+
+	if (!phydev->link)
+		return 0;
+
+	val = phy_read_paged(phydev, 0xa43, 0x12);
+	if (val < 0)
+		return val;
+
+	switch (val & RTLGEN_SPEED_MASK) {
+	case 0x0000:
+		phydev->speed = SPEED_10;
+		break;
+	case 0x0010:
+		phydev->speed = SPEED_100;
+		break;
+	case 0x0020:
+		phydev->speed = SPEED_1000;
+		break;
+	case 0x0200:
+		phydev->speed = SPEED_10000;
+		break;
+	case 0x0210:
+		phydev->speed = SPEED_2500;
+		break;
+	case 0x0220:
+		phydev->speed = SPEED_5000;
+		break;
+	default:
+		break;
+	}
+
+	return 0;
+}
+
+static int rtlgen_read_status(struct phy_device *phydev)
+{
+	int ret;
+
+	ret = genphy_read_status(phydev);
+	if (ret < 0)
+		return ret;
+
+	return rtlgen_get_speed(phydev);
+}
+
 static int rtlgen_read_mmd(struct phy_device *phydev, int devnum, u16 regnum)
 {
 	int ret;
@@ -429,6 +480,8 @@ static int rtl8125_config_aneg(struct phy_device *phydev)
 
 static int rtl8125_read_status(struct phy_device *phydev)
 {
+	int ret;
+
 	if (phydev->autoneg == AUTONEG_ENABLE) {
 		int lpadv = phy_read_paged(phydev, 0xa5d, 0x13);
 
@@ -443,7 +496,11 @@ static int rtl8125_read_status(struct phy_device *phydev)
 			phydev->lp_advertising, lpadv & RTL_LPADV_2500FULL);
 	}
 
-	return genphy_read_status(phydev);
+	ret = genphy_read_status(phydev);
+	if (ret < 0)
+		return ret;
+
+	return rtlgen_get_speed(phydev);
 }
 
 static bool rtlgen_supports_2_5gbps(struct phy_device *phydev)
@@ -550,6 +607,7 @@ static struct phy_driver realtek_drvs[] = {
 	}, {
 		.name		= "Generic FE-GE Realtek PHY",
 		.match_phy_device = rtlgen_match_phy_device,
+		.read_status	= rtlgen_read_status,
 		.suspend	= genphy_suspend,
 		.resume		= genphy_resume,
 		.read_page	= rtl821x_read_page,