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+.. SPDX-License-Identifier: GPL-2.0-or-later
+.. Luigi 'Comio' Mantellini <luigi.mantellini@idf-hit.com>, Industrie Dial Face S.p.A., 2009
+
+Bit-banged MII bus support
+==========================
+
+The miiphybb ( Bit-banged MII bus driver ) supports an arbitrary number of
+MII buses. This feature is useful when a driver uses different MII buses for
+different PHYs and all (or a part) of these buses are implemented via
+bit-banging mode.
+
+The driver requires that the following macro is defined in the board
+configuration file:
+
+* CONFIG_BITBANGMII - Enable the miiphybb driver
+
+The driver code needs to allocate a regular MDIO device using mdio_alloc()
+and assign .read and .write accessors which wrap bb_miiphy_read() and
+bb_miiphy_write() functions respectively. The bb_miiphy_read() and
+bb_miiphy_write() functions take a pointer to a callback structure,
+struct bb_miiphy_bus_ops. The struct bb_miiphy_bus_ops has the following
+fields/callbacks (see miiphy.h for details):
+
+.. code-block:: c
+
+    int (*mdio_active)()   // Activate the MDIO pin as output
+    int (*mdio_tristate)() // Activate the MDIO pin as input/tristate pin
+    int (*set_mdio)()      // Write the MDIO pin
+    int (*get_mdio)()      // Read the MDIO pin
+    int (*set_mdc)()       // Write the MDC pin
+    int (*delay)()         // Delay function
+
+The driver code will look like:
+
+.. code-block:: c
+
+    static const struct bb_miiphy_bus_ops ravb_bb_miiphy_bus_ops = {
+        .mdio_active      = ravb_bb_mdio_active,
+        .mdio_tristate    = ravb_bb_mdio_tristate,
+        .set_mdio         = ravb_bb_set_mdio,
+        .get_mdio         = ravb_bb_get_mdio,
+        .set_mdc          = ravb_bb_set_mdc,
+        .delay            = ravb_bb_delay,
+    };
+
+    static int ravb_bb_miiphy_read(struct mii_dev *miidev, int addr,
+                                   int devad, int reg)
+    {
+        return bb_miiphy_read(miidev, &ravb_bb_miiphy_bus_ops,
+                              addr, devad, reg);
+    }
+
+    static int ravb_bb_miiphy_write(struct mii_dev *miidev, int addr,
+                                    int devad, int reg, u16 value)
+    {
+        return bb_miiphy_write(miidev, &ravb_bb_miiphy_bus_ops,
+                               addr, devad, reg, value);
+    }
+
+    static int ravb_probe(struct udevice *dev)
+    {
+        struct mii_dev *mdiodev;
+    ...
+        mdiodev = mdio_alloc();
+        if (!mdiodev)
+            return -ENOMEM;
+
+        mdiodev->read = ravb_bb_miiphy_read;
+        mdiodev->write = ravb_bb_miiphy_write;
+        mdiodev->priv = eth;
+        snprintf(mdiodev->name, sizeof(mdiodev->name), dev->name);
+
+        ret = mdio_register(mdiodev);
+    ...
+    }