[PATCH] mdio_bus: Issue GPIO RESET to PHYs.

[Roger Quadros]

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@xxxxxx>
---
 drivers/net/phy/mdio_bus.c | 26 ++++++++++++++++++++++++++
 drivers/of/of_mdio.c       |  4 ++++
 include/linux/phy.h        |  5 +++++
 3 files changed, 35 insertions(+)

diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
index fa7d51f..25fda2b 100644
--- a/drivers/net/phy/mdio_bus.c
+++ b/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>
@@ -43,6 +46,8 @@
 
 #include "mdio-boardinfo.h"
 
+#define DEFAULT_GPIO_RESET_DELAY	10	/* in microseconds */
+
 int mdiobus_register_device(struct mdio_device *mdiodev)
 {
 	if (mdiodev->bus->mdio_map[mdiodev->addr])
@@ -307,6 +312,7 @@ 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)
@@ -333,6 +339,26 @@ int __mdiobus_register(struct mii_bus *bus, struct module *owner)
 	if (bus->reset)
 		bus->reset(bus);
 
+	/* de-assert bus level PHY GPIO resets */
+	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) {
+				pr_err("mii_bus %s couldn't get reset GPIO\n",
+				       bus->id);
+				return err;
+			}
+		} else {
+			gpiod_set_value_cansleep(gpiod, 1);
+			if (!bus->reset_delay_us)
+				bus->reset_delay_us = DEFAULT_GPIO_RESET_DELAY;
+			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;
diff --git a/drivers/of/of_mdio.c b/drivers/of/of_mdio.c
index 0b29798..83a62e4 100644
--- a/drivers/of/of_mdio.c
+++ b/drivers/of/of_mdio.c
@@ -221,6 +221,10 @@ int of_mdiobus_register(struct mii_bus *mdio, struct device_node *np)
 
 	mdio->dev.of_node = np;
 
+	/* Get bus level PHY reset GPIO details */
+	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)
diff --git a/include/linux/phy.h b/include/linux/phy.h
index 43a7748..80a6574 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h
@@ -217,6 +217,11 @@ struct mii_bus {
 	 * matching its address
 	 */
 	int irq[PHY_MAX_ADDR];
+
+	/* GPIO reset pulse width in uS */
+	int reset_delay_us;
+	/* Number of reset GPIOs */
+	int num_reset_gpios;
 };
 #define to_mii_bus(d) container_of(d, struct mii_bus, dev)
 
-- 
2.7.4