ath79: ag71xx: add support for optional mdio reset

On ar933x and later chips, there are separated mac/mdio resets, but
resetting the entire gmac block with register values requires both
mac_reset and mdio_reset to be asserted together.

Add support for optional mdio reset so that we can do a full reset
if needed.

This patch also replaced deprecated devm_reset_control_get for
mac reset.

To use this feature, the following is needed:
 1. drop "simple-mfd" compatible to register mdio0 after gmac init
    so that mdio registers aren't reset after initialization.
 2. move mdio reset from mdio-bus to its parent eth node.

NOTE: This can't be applied on gmac1 with builtin switch since we
haven't add a feature to defer probe if phy connection failed.

Signed-off-by: Chuanhong Guo <gch981213@gmail.com>

target/linux/ath79/files/drivers/net/ethernet/atheros/ag71xx/ag71xx.h

@@ -188,6 +188,7 @@ struct ag71xx {
 	struct timer_list	oom_timer;
 
 	struct reset_control *mac_reset;
+	struct reset_control *mdio_reset;
 
 	u32			fifodata[3];
 	u32			plldata[3];

target/linux/ath79/files/drivers/net/ethernet/atheros/ag71xx/ag71xx_main.c

@@ -453,8 +453,12 @@ static void ag71xx_hw_init(struct ag71xx *ag)
 	udelay(20);
 
 	reset_control_assert(ag->mac_reset);
+	if (ag->mdio_reset)
+		reset_control_assert(ag->mdio_reset);
 	msleep(100);
 	reset_control_deassert(ag->mac_reset);
+	if (ag->mdio_reset)
+		reset_control_deassert(ag->mdio_reset);
 	msleep(200);
 
 	ag71xx_hw_setup(ag);
@@ -1352,12 +1356,14 @@ static int ag71xx_probe(struct platform_device *pdev)
 					AG71XX_DEFAULT_MSG_ENABLE);
 	spin_lock_init(&ag->lock);
 
-	ag->mac_reset = devm_reset_control_get(&pdev->dev, "mac");
+	ag->mac_reset = devm_reset_control_get_exclusive(&pdev->dev, "mac");
 	if (IS_ERR(ag->mac_reset)) {
 		dev_err(&pdev->dev, "missing mac reset\n");
 		return PTR_ERR(ag->mac_reset);
 	}
 
+	ag->mdio_reset = devm_reset_control_get_optional_exclusive(&pdev->dev, "mdio");
+
 	if (of_property_read_u32_array(np, "fifo-data", ag->fifodata, 3)) {
 		if (of_device_is_compatible(np, "qca,ar9130-eth") ||
 		    of_device_is_compatible(np, "qca,ar7100-eth")) {