i2c: add i2c_trylock_bus wrapper, use it

This unifies usage with i2c_lock_bus and i2c_unlock_bus, and paves the
way for the next patch which looks a bit saner with this preparatory
work taken care of beforehand.
Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/i2c/i2c-core.c

@@ -2459,7 +2459,7 @@ int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
 #endif
 
 		if (in_atomic() || irqs_disabled()) {
-			ret = adap->trylock_bus(adap, I2C_LOCK_SEGMENT);
+			ret = i2c_trylock_bus(adap, I2C_LOCK_SEGMENT);
 			if (!ret)
 				/* I2C activity is ongoing. */
 				return -EAGAIN;

drivers/i2c/i2c-mux.c

@@ -159,7 +159,7 @@ static int i2c_mux_trylock_bus(struct i2c_adapter *adapter, unsigned int flags)
 		return 0;	/* mux_lock not locked, failure */
 	if (!(flags & I2C_LOCK_ROOT_ADAPTER))
 		return 1;	/* we only want mux_lock, success */
-	if (parent->trylock_bus(parent, flags))
+	if (i2c_trylock_bus(parent, flags))
 		return 1;	/* parent locked too, success */
 	rt_mutex_unlock(&parent->mux_lock);
 	return 0;		/* parent not locked, failure */
@@ -193,7 +193,7 @@ static int i2c_parent_trylock_bus(struct i2c_adapter *adapter,
 
 	if (!rt_mutex_trylock(&parent->mux_lock))
 		return 0;	/* mux_lock not locked, failure */
-	if (parent->trylock_bus(parent, flags))
+	if (i2c_trylock_bus(parent, flags))
 		return 1;	/* parent locked too, success */
 	rt_mutex_unlock(&parent->mux_lock);
 	return 0;		/* parent not locked, failure */

include/linux/i2c.h

@@ -600,6 +600,20 @@ i2c_lock_bus(struct i2c_adapter *adapter, unsigned int flags)
 	adapter->lock_bus(adapter, flags);
 }
 
+/**
+ * i2c_trylock_bus - Try to get exclusive access to an I2C bus segment
+ * @adapter: Target I2C bus segment
+ * @flags: I2C_LOCK_ROOT_ADAPTER tries to locks the root i2c adapter,
+ *	I2C_LOCK_SEGMENT tries to lock only this branch in the adapter tree
+ *
+ * Return: true if the I2C bus segment is locked, false otherwise
+ */
+static inline int
+i2c_trylock_bus(struct i2c_adapter *adapter, unsigned int flags)
+{
+	return adapter->trylock_bus(adapter, flags);
+}
+
 /**
  * i2c_unlock_bus - Release exclusive access to an I2C bus segment
  * @adapter: Target I2C bus segment