dsa: mv88e6xxx.c: Hardware reset the chip if available

The device tree binding now allows a gpio to be specified which is
attached to the switch chips reset line. If it is defined, perform
a hardware reset on the switch during setup.
Signed-off-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx.c

@@ -19,6 +19,7 @@
 #include <linux/list.h>
 #include <linux/module.h>
 #include <linux/netdevice.h>
+#include <linux/gpio/consumer.h>
 #include <linux/phy.h>
 #include <net/dsa.h>
 #include <net/switchdev.h>
@@ -2323,6 +2324,7 @@ int mv88e6xxx_switch_reset(struct dsa_switch *ds, bool ppu_active)
 {
 	struct mv88e6xxx_priv_state *ps = ds_to_priv(ds);
 	u16 is_reset = (ppu_active ? 0x8800 : 0xc800);
+	struct gpio_desc *gpiod = ds->pd->reset;
 	unsigned long timeout;
 	int ret;
 	int i;
@@ -2336,6 +2338,14 @@ int mv88e6xxx_switch_reset(struct dsa_switch *ds, bool ppu_active)
 	/* Wait for transmit queues to drain. */
 	usleep_range(2000, 4000);
 
+	/* If there is a gpio connected to the reset pin, toggle it */
+	if (gpiod) {
+		gpiod_set_value_cansleep(gpiod, 1);
+		usleep_range(10000, 20000);
+		gpiod_set_value_cansleep(gpiod, 0);
+		usleep_range(10000, 20000);
+	}
+
 	/* Reset the switch. Keep the PPU active if requested. The PPU
 	 * needs to be active to support indirect phy register access
 	 * through global registers 0x18 and 0x19.