usb: musb: core: add common method of getting vbus status

Fix musb_platform_get_vbus_status return value in case of platform
implementation is not defined, bringing expected behaviour of
musb_platform_get wrapper. Add musb_vbus_show default method to determine
VBUS status in case platform method is not defined.
Signed-off-by: Roman Alyautdin <ralyautdin@dev.rtsoft.ru>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/musb/musb_core.c

@@ -1775,13 +1775,20 @@ musb_vbus_show(struct device *dev, struct device_attribute *attr, char *buf)
 	unsigned long	flags;
 	unsigned long	val;
 	int		vbus;
+	u8		devctl;
 
 	spin_lock_irqsave(&musb->lock, flags);
 	val = musb->a_wait_bcon;
-	/* FIXME get_vbus_status() is normally #defined as false...
-	 * and is effectively TUSB-specific.
-	 */
 	vbus = musb_platform_get_vbus_status(musb);
+	if (vbus < 0) {
+		/* Use default MUSB method by means of DEVCTL register */
+		devctl = musb_readb(musb->mregs, MUSB_DEVCTL);
+		if ((devctl & MUSB_DEVCTL_VBUS)
+				== (3 << MUSB_DEVCTL_VBUS_SHIFT))
+			vbus = 1;
+		else
+			vbus = 0;
+	}
 	spin_unlock_irqrestore(&musb->lock, flags);
 
 	return sprintf(buf, "Vbus %s, timeout %lu msec\n",

drivers/usb/musb/musb_core.h

@@ -579,7 +579,7 @@ static inline int  musb_platform_recover(struct musb *musb)
 static inline int musb_platform_get_vbus_status(struct musb *musb)
 {
 	if (!musb->ops->vbus_status)
-		return 0;
+		return -EINVAL;
 
 	return musb->ops->vbus_status(musb);
 }