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>
diff --git a/drivers/net/sfc/sfe4001.c b/drivers/net/sfc/sfe4001.c
index cee00ad..49eb91b 100644
--- a/drivers/net/sfc/sfe4001.c
+++ b/drivers/net/sfc/sfe4001.c
@@ -188,7 +188,7 @@
 	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 @@
 	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;