mdio_bus: Issue GPIO RESET to PHYs.

Some boards [1] leave the PHYs at an invalid state
during system power-up or reset thus causing unreliability
issues with the PHY which manifests as PHY not being detected
or link not functional. To fix this, these PHYs need to be RESET
via a GPIO connected to the PHY's RESET pin.

Some boards have a single GPIO controlling the PHY RESET pin of all
PHYs on the bus whereas some others have separate GPIOs controlling
individual PHY RESETs.

In both cases, the RESET de-assertion cannot be done in the PHY driver
as the PHY will not probe till its reset is de-asserted.
So do the RESET de-assertion in the MDIO bus driver.

[1] - am572x-idk, am571x-idk, a437x-idk

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/mdio.txt

@@ -0,0 +1,33 @@
+Common MDIO bus properties.
+
+These are generic properties that can apply to any MDIO bus.
+
+Optional properties:
+- reset-gpios: List of one or more GPIOs that control the RESET lines
+  of the PHYs on that MDIO bus.
+- reset-delay-us: RESET pulse width in microseconds as per PHY datasheet.
+
+A list of child nodes, one per device on the bus is expected. These
+should follow the generic phy.txt, or a device specific binding document.
+
+Example :
+This example shows these optional properties, plus other properties
+required for the TI Davinci MDIO driver.
+
+	davinci_mdio: ethernet@0x5c030000 {
+		compatible = "ti,davinci_mdio";
+		reg = <0x5c030000 0x1000>;
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		reset-gpios = <&gpio2 5 GPIO_ACTIVE_LOW>;
+		reset-delay-us = <2>;   /* PHY datasheet states 1us min */
+
+		ethphy0: ethernet-phy@1 {
+			reg = <1>;
+		};
+
+		ethphy1: ethernet-phy@3 {
+			reg = <3>;
+		};
+	};

drivers/net/phy/mdio_bus.c

@@ -22,8 +22,11 @@
 #include <linux/init.h>
 #include <linux/delay.h>
 #include <linux/device.h>
+#include <linux/gpio.h>
+#include <linux/gpio/consumer.h>
 #include <linux/of_device.h>
 #include <linux/of_mdio.h>
+#include <linux/of_gpio.h>
 #include <linux/netdevice.h>
 #include <linux/etherdevice.h>
 #include <linux/skbuff.h>
@@ -337,6 +340,7 @@ int __mdiobus_register(struct mii_bus *bus, struct module *owner)
 {
 	struct mdio_device *mdiodev;
 	int i, err;
+	struct gpio_desc *gpiod;
 
 	if (NULL == bus || NULL == bus->name ||
 	    NULL == bus->read || NULL == bus->write)
@@ -363,6 +367,35 @@ int __mdiobus_register(struct mii_bus *bus, struct module *owner)
 	if (bus->reset)
 		bus->reset(bus);
 
+	/* de-assert bus level PHY GPIO resets */
+	if (bus->num_reset_gpios > 0) {
+		bus->reset_gpiod = devm_kcalloc(&bus->dev,
+						 bus->num_reset_gpios,
+						 sizeof(struct gpio_desc *),
+						 GFP_KERNEL);
+		if (!bus->reset_gpiod)
+			return -ENOMEM;
+	}
+
+	for (i = 0; i < bus->num_reset_gpios; i++) {
+		gpiod = devm_gpiod_get_index(&bus->dev, "reset", i,
+					     GPIOD_OUT_LOW);
+		if (IS_ERR(gpiod)) {
+			err = PTR_ERR(gpiod);
+			if (err != -ENOENT) {
+				dev_err(&bus->dev,
+					"mii_bus %s couldn't get reset GPIO\n",
+					bus->id);
+				return err;
+			}
+		} else {
+			bus->reset_gpiod[i] = gpiod;
+			gpiod_set_value_cansleep(gpiod, 1);
+			udelay(bus->reset_delay_us);
+			gpiod_set_value_cansleep(gpiod, 0);
+		}
+	}
+
 	for (i = 0; i < PHY_MAX_ADDR; i++) {
 		if ((bus->phy_mask & (1 << i)) == 0) {
 			struct phy_device *phydev;
@@ -390,6 +423,13 @@ error:
 		mdiodev->device_remove(mdiodev);
 		mdiodev->device_free(mdiodev);
 	}
+
+	/* Put PHYs in RESET to save power */
+	for (i = 0; i < bus->num_reset_gpios; i++) {
+		if (bus->reset_gpiod[i])
+			gpiod_set_value_cansleep(bus->reset_gpiod[i], 1);
+	}
+
 	device_del(&bus->dev);
 	return err;
 }
@@ -411,6 +451,13 @@ void mdiobus_unregister(struct mii_bus *bus)
 		mdiodev->device_remove(mdiodev);
 		mdiodev->device_free(mdiodev);
 	}
+
+	/* Put PHYs in RESET to save power */
+	for (i = 0; i < bus->num_reset_gpios; i++) {
+		if (bus->reset_gpiod[i])
+			gpiod_set_value_cansleep(bus->reset_gpiod[i], 1);
+	}
+
 	device_del(&bus->dev);
 }
 EXPORT_SYMBOL(mdiobus_unregister);

drivers/of/of_mdio.c

@@ -22,6 +22,8 @@
 #include <linux/of_net.h>
 #include <linux/module.h>
 
+#define DEFAULT_GPIO_RESET_DELAY	10	/* in microseconds */
+
 MODULE_AUTHOR("Grant Likely <grant.likely@secretlab.ca>");
 MODULE_LICENSE("GPL");
 
@@ -221,6 +223,11 @@ int of_mdiobus_register(struct mii_bus *mdio, struct device_node *np)
 
 	mdio->dev.of_node = np;
 
+	/* Get bus level PHY reset GPIO details */
+	mdio->reset_delay_us = DEFAULT_GPIO_RESET_DELAY;
+	of_property_read_u32(np, "reset-delay-us", &mdio->reset_delay_us);
+	mdio->num_reset_gpios = of_gpio_named_count(np, "reset-gpios");
+
 	/* Register the MDIO bus */
 	rc = mdiobus_register(mdio);
 	if (rc)

include/linux/phy.h

@@ -217,6 +217,13 @@ struct mii_bus {
 	 * matching its address
 	 */
 	int irq[PHY_MAX_ADDR];
+
+	/* GPIO reset pulse width in microseconds */
+	int reset_delay_us;
+	/* Number of reset GPIOs */
+	int num_reset_gpios;
+	/* Array of RESET GPIO descriptors */
+	struct gpio_desc **reset_gpiod;
 };
 #define to_mii_bus(d) container_of(d, struct mii_bus, dev)