net: phy: Optionally force master mode for RTL PHY

This patch introduces CONFIG_RTL8211X_PHY_FORCE_MASTER. If this
define is set, RTL8211x PHYs (except for the RTL8211F) will have their
1000BASE-T master/slave autonegotiation disabled and forced to master
mode.

This is helpful for PHYs like the RTL8211C which produce unstable links
in slave mode. Such problems have been found on the A20-Olimex-SOM-EVB
and A20-OLinuXino-Lime2.

There is no proper way to identify affected PHYs in software as the
RTL8211C shares its UID with the RTL8211B. Thus, this fix requires
the introduction of an #ifdef.

CC: fradav@gmail.com
CC: merker@debian.org
CC: hdegoede@redhat.com
CC: ijc@hellion.org.uk
CC: joe.hershberger@ni.com

Signed-off-by: Michael Haas <haas@computerlinguist.org>
Tested-by: Karsten Merker <merker@debian.org>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/net/Kconfig

@@ -13,6 +13,27 @@ config PHYLIB
 	help
 	  Enable Ethernet PHY (physical media interface) support.
 
+config RTL8211X_PHY_FORCE_MASTER
+	bool "Ethernet PHY RTL8211x: force 1000BASE-T master mode"
+	depends on PHYLIB
+	help
+	  Force master mode for 1000BASE-T on RTl8211x PHYs (except for RTL8211F).
+	  This can work around link stability and data corruption issues on gigabit
+	  links which can occur in slave mode on certain PHYs, e.g. on the
+	  RTL8211C(L).
+
+	  Please note that two directly connected devices (i.e. via crossover cable)
+	  will not be able to establish a link between each other if they both force
+	  master mode. Multiple devices forcing master mode when connected by a
+	  network switch do not pose a problem as the switch configures its affected
+	  ports into slave mode.
+
+	  This option only affects gigabit links. If you must establish a direct
+	  connection between two devices which both force master mode, try forcing
+	  the link speed to 100MBit/s.
+
+	  If unsure, say N.
+
 menuconfig NETDEVICES
 	bool "Network device support"
 	depends on NET

drivers/net/phy/realtek.c

@@ -12,6 +12,10 @@
 
 #define PHY_AUTONEGOTIATE_TIMEOUT 5000
 
+/* RTL8211x 1000BASE-T Control Register */
+#define MIIM_RTL8211x_CTRL1000T_MSCE (1 << 12);
+#define MIIM_RTL8211X_CTRL1000T_MASTER (1 << 11);
+
 /* RTL8211x PHY Status Register */
 #define MIIM_RTL8211x_PHY_STATUS       0x11
 #define MIIM_RTL8211x_PHYSTAT_SPEED    0xc000
@@ -53,7 +57,14 @@ static int rtl8211x_config(struct phy_device *phydev)
 	 */
 	phy_write(phydev, MDIO_DEVAD_NONE, MIIM_RTL8211x_PHY_INER,
 		  MIIM_RTL8211x_PHY_INTR_DIS);
-
+#ifdef CONFIG_RTL8211X_PHY_FORCE_MASTER
+	unsigned int reg = phy_read(phydev, MDIO_DEVAD_NONE, MII_CTRL1000);
+	/* force manual master/slave configuration */
+	reg |= MIIM_RTL8211x_CTRL1000T_MSCE;
+	/* force master mode */
+	reg |= MIIM_RTL8211X_CTRL1000T_MASTER;
+	phy_write(phydev, MDIO_DEVAD_NONE, MII_CTRL1000, reg);
+#endif
 	/* read interrupt status just to clear it */
 	phy_read(phydev, MDIO_DEVAD_NONE, MIIM_RTL8211x_PHY_INER);