net: dsa: mv88e6xxx: introduce support for two chips using direct smi addressing

The 88e6250 (as well as 6220, 6071, 6070, 6020) do not support
multi-chip (indirect) addressing. However, one can still have two of
them on the same mdio bus, since the device only uses 16 of the 32
possible addresses, either addresses 0x00-0x0F or 0x10-0x1F depending
on the ADDR4 pin at reset [since ADDR4 is internally pulled high, the
latter is the default].

In order to prepare for supporting the 88e6250 and friends, introduce
mv88e6xxx_info::dual_chip to allow having a non-zero sw_addr while
still using direct addressing.
Reviewed-by: Vivien Didelot <vivien.didelot@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/chip.h

@@ -112,6 +112,12 @@ struct mv88e6xxx_info {
 	 * when it is non-zero, and use indirect access to internal registers.
 	 */
 	bool multi_chip;
+	/* Dual-chip Addressing Mode
+	 * Some chips respond to only half of the 32 SMI addresses,
+	 * allowing two to coexist on the same SMI interface.
+	 */
+	bool dual_chip;
+
 	enum dsa_tag_protocol tag_protocol;
 
 	/* Mask for FromPort and ToPort value of PortVec used in ATU Move

drivers/net/dsa/mv88e6xxx/smi.c

@@ -24,6 +24,10 @@
  * When ADDR is non-zero, the chip uses Multi-chip Addressing Mode, allowing
  * multiple devices to share the SMI interface. In this mode it responds to only
  * 2 registers, used to indirectly access the internal SMI devices.
+ *
+ * Some chips use a different scheme: Only the ADDR4 pin is used for
+ * configuration, and the device responds to 16 of the 32 SMI
+ * addresses, allowing two to coexist on the same SMI interface.
  */
 
 static int mv88e6xxx_smi_direct_read(struct mv88e6xxx_chip *chip,
@@ -76,6 +80,23 @@ static const struct mv88e6xxx_bus_ops mv88e6xxx_smi_direct_ops = {
 	.write = mv88e6xxx_smi_direct_write,
 };
 
+static int mv88e6xxx_smi_dual_direct_read(struct mv88e6xxx_chip *chip,
+					  int dev, int reg, u16 *data)
+{
+	return mv88e6xxx_smi_direct_read(chip, chip->sw_addr + dev, reg, data);
+}
+
+static int mv88e6xxx_smi_dual_direct_write(struct mv88e6xxx_chip *chip,
+					   int dev, int reg, u16 data)
+{
+	return mv88e6xxx_smi_direct_write(chip, chip->sw_addr + dev, reg, data);
+}
+
+static const struct mv88e6xxx_bus_ops mv88e6xxx_smi_dual_direct_ops = {
+	.read = mv88e6xxx_smi_dual_direct_read,
+	.write = mv88e6xxx_smi_dual_direct_write,
+};
+
 /* Offset 0x00: SMI Command Register
  * Offset 0x01: SMI Data Register
  */
@@ -144,7 +165,9 @@ static const struct mv88e6xxx_bus_ops mv88e6xxx_smi_indirect_ops = {
 int mv88e6xxx_smi_init(struct mv88e6xxx_chip *chip,
 		       struct mii_bus *bus, int sw_addr)
 {
-	if (sw_addr == 0)
+	if (chip->info->dual_chip)
+		chip->smi_ops = &mv88e6xxx_smi_dual_direct_ops;
+	else if (sw_addr == 0)
 		chip->smi_ops = &mv88e6xxx_smi_direct_ops;
 	else if (chip->info->multi_chip)
 		chip->smi_ops = &mv88e6xxx_smi_indirect_ops;