usb: phy: am335x-control: wait 1ms after power-up transitions

Tests have shown that when a power-up transition is followed by other
PHY operations too quickly, the USB port appears dead. Waiting 1ms fixes
this problem.

Signed-off-by: Daniel Mack <[e-mail]>
Cc: [e-mail] [3.14]
Signed-off-by: Felipe Balbi <[e-mail]>

drivers/usb/phy/phy-am335x-control.c

···
 #include <linux/err.h>
 #include <linux/of.h>
 #include <linux/io.h>
+#include <linux/delay.h>
 #include "am35x-phy-control.h"
 
 struct am335x_control_usb {
···
 	}
 
 	writel(val, usb_ctrl->phy_reg + reg);
+
+	/*
+	 * Give the PHY ~1ms to complete the power up operation.
+	 * Tests have shown unstable behaviour if other USB PHY related
+	 * registers are written too shortly after such a transition.
+	 */
+	if (on)
+		mdelay(1);
 }
 
 static const struct phy_control ctrl_am335x = {