i2c: Add an interface to lock/unlock an I2C bus segment

Some drivers need to be able to prevent access to an I2C bus segment
for a specific period of time. Add an interface for them to do so
without twiddling with i2c-core internals.
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Ben Hutchings <bhutchings@solarflare.com>

drivers/net/sfc/sfe4001.c

@@ -188,7 +188,7 @@ static int sfn4111t_reset(struct efx_nic *efx)
 	efx_oword_t reg;
 
 	/* GPIO 3 and the GPIO register are shared with I2C, so block that */
-	mutex_lock(&efx->i2c_adap.bus_lock);
+	i2c_lock_adapter(&efx->i2c_adap);
 
 	/* Pull RST_N (GPIO 2) low then let it up again, setting the
 	 * FLASH_CFG_1 strap (GPIO 3) appropriately.  Only change the
@@ -204,7 +204,7 @@ static int sfn4111t_reset(struct efx_nic *efx)
 	falcon_write(efx, &reg, GPIO_CTL_REG_KER);
 	msleep(1);
 
-	mutex_unlock(&efx->i2c_adap.bus_lock);
+	i2c_unlock_adapter(&efx->i2c_adap);
 
 	ssleep(1);
 	return 0;

include/linux/i2c.h

@@ -361,6 +361,24 @@ static inline void i2c_set_adapdata(struct i2c_adapter *dev, void *data)
 	dev_set_drvdata(&dev->dev, data);
 }
 
+/**
+ * i2c_lock_adapter - Prevent access to an I2C bus segment
+ * @adapter: Target I2C bus segment
+ */
+static inline void i2c_lock_adapter(struct i2c_adapter *adapter)
+{
+	mutex_lock(&adapter->bus_lock);
+}
+
+/**
+ * i2c_unlock_adapter - Reauthorize access to an I2C bus segment
+ * @adapter: Target I2C bus segment
+ */
+static inline void i2c_unlock_adapter(struct i2c_adapter *adapter)
+{
+	mutex_unlock(&adapter->bus_lock);
+}
+
 /*flags for the client struct: */
 #define I2C_CLIENT_PEC	0x04		/* Use Packet Error Checking */
 #define I2C_CLIENT_TEN	0x10		/* we have a ten bit chip address */