i2c: recovery: if possible send STOP with recovery pulses

I2C clients may misunderstand recovery pulses if they can't read SDA to
bail out early. In the worst case, as a write operation. To avoid that
and if we can write SDA, try to send STOP to avoid the
misinterpretation.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: stable@kernel.org

drivers/i2c/i2c-core-base.c

@@ -198,7 +198,16 @@ int i2c_generic_scl_recovery(struct i2c_adapter *adap)
 
 		val = !val;
 		bri->set_scl(adap, val);
-		ndelay(RECOVERY_NDELAY);
+
+		/*
+		 * If we can set SDA, we will always create STOP here to ensure
+		 * the additional pulses will do no harm. This is achieved by
+		 * letting SDA follow SCL half a cycle later.
+		 */
+		ndelay(RECOVERY_NDELAY / 2);
+		if (bri->set_sda)
+			bri->set_sda(adap, val);
+		ndelay(RECOVERY_NDELAY / 2);
 	}
 
 	/* check if recovery actually succeeded */