net: phy: Add support for microchip SMI0 MDIO bus

SMI0 is a mangled version of MDIO. The main low level difference is
the MDIO C22 OP code is always 0, not 0x2 or 0x1 for Read/Write. The
read/write information is instead encoded in the PHY address.

Extend the bit-bang code to allow the op code to be overridden, but
default to normal C22 values. Add an extra compatible to the mdio-gpio
driver, and when this compatible is present, set the op codes to 0.

A higher level driver, sitting on top of the basic MDIO bus driver can
then implement the rest of the microchip SMI0 odderties.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/mdio/mdio-bitbang.c

@@ -158,7 +158,7 @@ int mdiobb_read(struct mii_bus *bus, int phy, int reg)
 		reg = mdiobb_cmd_addr(ctrl, phy, reg);
 		mdiobb_cmd(ctrl, MDIO_C45_READ, phy, reg);
 	} else
-		mdiobb_cmd(ctrl, MDIO_READ, phy, reg);
+		mdiobb_cmd(ctrl, ctrl->op_c22_read, phy, reg);
 
 	ctrl->ops->set_mdio_dir(ctrl, 0);
 
@@ -190,7 +190,7 @@ int mdiobb_write(struct mii_bus *bus, int phy, int reg, u16 val)
 		reg = mdiobb_cmd_addr(ctrl, phy, reg);
 		mdiobb_cmd(ctrl, MDIO_C45_WRITE, phy, reg);
 	} else
-		mdiobb_cmd(ctrl, MDIO_WRITE, phy, reg);
+		mdiobb_cmd(ctrl, ctrl->op_c22_write, phy, reg);
 
 	/* send the turnaround (10) */
 	mdiobb_send_bit(ctrl, 1);
@@ -217,6 +217,10 @@ struct mii_bus *alloc_mdio_bitbang(struct mdiobb_ctrl *ctrl)
 	bus->read = mdiobb_read;
 	bus->write = mdiobb_write;
 	bus->priv = ctrl;
+	if (!ctrl->override_op_c22) {
+		ctrl->op_c22_read = MDIO_READ;
+		ctrl->op_c22_write = MDIO_WRITE;
+	}
 
 	return bus;
 }

drivers/net/mdio/mdio-gpio.c

@@ -132,6 +132,13 @@ static struct mii_bus *mdio_gpio_bus_init(struct device *dev,
 		new_bus->phy_ignore_ta_mask = pdata->phy_ignore_ta_mask;
 	}
 
+	if (dev->of_node &&
+	    of_device_is_compatible(dev->of_node, "microchip,mdio-smi0")) {
+		bitbang->ctrl.op_c22_read = 0;
+		bitbang->ctrl.op_c22_write = 0;
+		bitbang->ctrl.override_op_c22 = 1;
+	}
+
 	dev_set_drvdata(dev, new_bus);
 
 	return new_bus;
@@ -196,6 +203,7 @@ static int mdio_gpio_remove(struct platform_device *pdev)
 
 static const struct of_device_id mdio_gpio_of_match[] = {
 	{ .compatible = "virtual,mdio-gpio", },
+	{ .compatible = "microchip,mdio-smi0" },
 	{ /* sentinel */ }
 };
 MODULE_DEVICE_TABLE(of, mdio_gpio_of_match);

include/linux/mdio-bitbang.h

@@ -33,6 +33,9 @@ struct mdiobb_ops {
 
 struct mdiobb_ctrl {
 	const struct mdiobb_ops *ops;
+	unsigned int override_op_c22;
+	u8 op_c22_read;
+	u8 op_c22_write;
 };
 
 int mdiobb_read(struct mii_bus *bus, int phy, int reg);