net: dsa: microchip: Add drive strength configuration

Add device tree based drive strength configuration support. It is needed to
pass EMI validation on our hardware.

Configuration values are based on the vendor's reference driver.

Tested on KSZ9563R.
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/microchip/ksz8795_reg.h

@@ -442,20 +442,6 @@
 #define TOS_PRIO_M			KS_PRIO_M
 #define TOS_PRIO_S			KS_PRIO_S
 
-#define REG_SW_CTRL_20			0xA3
-
-#define SW_GMII_DRIVE_STRENGTH_S	4
-#define SW_DRIVE_STRENGTH_M		0x7
-#define SW_DRIVE_STRENGTH_2MA		0
-#define SW_DRIVE_STRENGTH_4MA		1
-#define SW_DRIVE_STRENGTH_8MA		2
-#define SW_DRIVE_STRENGTH_12MA		3
-#define SW_DRIVE_STRENGTH_16MA		4
-#define SW_DRIVE_STRENGTH_20MA		5
-#define SW_DRIVE_STRENGTH_24MA		6
-#define SW_DRIVE_STRENGTH_28MA		7
-#define SW_MII_DRIVE_STRENGTH_S		0
-
 #define REG_SW_CTRL_21			0xA4
 
 #define SW_IPV6_MLD_OPTION		BIT(3)

drivers/net/dsa/microchip/ksz9477_reg.h

@@ -112,19 +112,6 @@
 
 #define REG_SW_IBA_SYNC__1		0x010C
 
-#define REG_SW_IO_STRENGTH__1		0x010D
-#define SW_DRIVE_STRENGTH_M		0x7
-#define SW_DRIVE_STRENGTH_2MA		0
-#define SW_DRIVE_STRENGTH_4MA		1
-#define SW_DRIVE_STRENGTH_8MA		2
-#define SW_DRIVE_STRENGTH_12MA		3
-#define SW_DRIVE_STRENGTH_16MA		4
-#define SW_DRIVE_STRENGTH_20MA		5
-#define SW_DRIVE_STRENGTH_24MA		6
-#define SW_DRIVE_STRENGTH_28MA		7
-#define SW_HI_SPEED_DRIVE_STRENGTH_S	4
-#define SW_LO_SPEED_DRIVE_STRENGTH_S	0
-
 #define REG_SW_IBA_STATUS__4		0x0110
 
 #define SW_IBA_REQ			BIT(31)

drivers/net/dsa/microchip/ksz_common.h

@@ -689,6 +689,26 @@ static inline int is_lan937x(struct ksz_device *dev)
 #define KSZ8_LEGAL_PACKET_SIZE		1518
 #define KSZ9477_MAX_FRAME_SIZE		9000
 
+#define KSZ8873_REG_GLOBAL_CTRL_12	0x0e
+/* Drive Strength of I/O Pad
+ * 0: 8mA, 1: 16mA
+ */
+#define KSZ8873_DRIVE_STRENGTH_16MA	BIT(6)
+
+#define KSZ8795_REG_SW_CTRL_20		0xa3
+#define KSZ9477_REG_SW_IO_STRENGTH	0x010d
+#define SW_DRIVE_STRENGTH_M		0x7
+#define SW_DRIVE_STRENGTH_2MA		0
+#define SW_DRIVE_STRENGTH_4MA		1
+#define SW_DRIVE_STRENGTH_8MA		2
+#define SW_DRIVE_STRENGTH_12MA		3
+#define SW_DRIVE_STRENGTH_16MA		4
+#define SW_DRIVE_STRENGTH_20MA		5
+#define SW_DRIVE_STRENGTH_24MA		6
+#define SW_DRIVE_STRENGTH_28MA		7
+#define SW_HI_SPEED_DRIVE_STRENGTH_S	4
+#define SW_LO_SPEED_DRIVE_STRENGTH_S	0
+
 #define KSZ9477_REG_PORT_OUT_RATE_0	0x0420
 #define KSZ9477_OUT_RATE_NO_LIMIT	0