net/macb: add support for resetting PHY using GPIO

With device tree it is no more possible to reset the PHY at board
level. Furthermore, doing in the driver allow to power down the PHY when
the network interface is no more used.

This reset can't be done at the PHY driver level. The PHY must be able to
answer the to the mii bus scan to let the kernel creating a PHY device.

The patch introduces a new optional property "phy-reset-gpios" inspired
from the one use for the FEC.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/macb.txt

@@ -19,6 +19,9 @@ Required properties:
 	Optional elements: 'tx_clk'
 - clocks: Phandles to input clocks.
 
+Optional properties:
+- phy-reset-gpios : Should specify the gpio for phy reset
+
 Examples:
 
 	macb0: ethernet@fffc4000 {

drivers/net/ethernet/cadence/macb.c

@@ -2904,6 +2904,10 @@ static int macb_probe(struct platform_device *pdev)
 	else
 		macb_get_hwaddr(bp);
 
+	/* Power up the PHY if there is a GPIO reset */
+	bp->reset_gpio = devm_gpiod_get_optional(&bp->pdev->dev, "phy-reset",
+						 GPIOD_OUT_HIGH);
+
 	err = of_get_phy_mode(np);
 	if (err < 0) {
 		pdata = dev_get_platdata(&pdev->dev);
@@ -2970,6 +2974,10 @@ static int macb_remove(struct platform_device *pdev)
 		mdiobus_unregister(bp->mii_bus);
 		kfree(bp->mii_bus->irq);
 		mdiobus_free(bp->mii_bus);
+
+		/* Shutdown the PHY if there is a GPIO reset */
+		gpiod_set_value(bp->reset_gpio, 0);
+
 		unregister_netdev(dev);
 		clk_disable_unprepare(bp->tx_clk);
 		clk_disable_unprepare(bp->hclk);

drivers/net/ethernet/cadence/macb.h

@@ -829,6 +829,7 @@ struct macb {
 	unsigned int		dma_burst_length;
 
 	phy_interface_t		phy_interface;
+	struct gpio_desc	*reset_gpio;
 
 	/* AT91RM9200 transmit */
 	struct sk_buff *skb;			/* holds skb until xmit interrupt completes */