soundwire: bus: clock_stop: don't deal with UNATTACHED Slave devices

We don't need to do anything for the slave if it is unattached during
clock stop prepare and exit sequences.
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Link: https://lore.kernel.org/r/20200531151806.25951-1-yung-chuan.liao@linux.intel.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soundwire/bus.c

@@ -863,13 +863,13 @@ int sdw_bus_prep_clk_stop(struct sdw_bus *bus)
 		if (!slave->dev_num)
 			continue;
 
-		/* Identify if Slave(s) are available on Bus */
-		is_slave = true;
-
 		if (slave->status != SDW_SLAVE_ATTACHED &&
 		    slave->status != SDW_SLAVE_ALERT)
 			continue;
 
+		/* Identify if Slave(s) are available on Bus */
+		is_slave = true;
+
 		slave_mode = sdw_get_clk_stop_mode(slave);
 		slave->curr_clk_stop_mode = slave_mode;
 
@@ -900,6 +900,10 @@ int sdw_bus_prep_clk_stop(struct sdw_bus *bus)
 			return ret;
 	}
 
+	/* Don't need to inform slaves if there is no slave attached */
+	if (!is_slave)
+		return ret;
+
 	/* Inform slaves that prep is done */
 	list_for_each_entry(slave, &bus->slaves, node) {
 		if (!slave->dev_num)
@@ -985,13 +989,13 @@ int sdw_bus_exit_clk_stop(struct sdw_bus *bus)
 		if (!slave->dev_num)
 			continue;
 
-		/* Identify if Slave(s) are available on Bus */
-		is_slave = true;
-
 		if (slave->status != SDW_SLAVE_ATTACHED &&
 		    slave->status != SDW_SLAVE_ALERT)
 			continue;
 
+		/* Identify if Slave(s) are available on Bus */
+		is_slave = true;
+
 		mode = slave->curr_clk_stop_mode;
 
 		if (mode == SDW_CLK_STOP_MODE1) {
@@ -1016,6 +1020,13 @@ int sdw_bus_exit_clk_stop(struct sdw_bus *bus)
 	if (is_slave && !simple_clk_stop)
 		sdw_bus_wait_for_clk_prep_deprep(bus, SDW_BROADCAST_DEV_NUM);
 
+	/*
+	 * Don't need to call slave callback function if there is no slave
+	 * attached
+	 */
+	if (!is_slave)
+		return 0;
+
 	list_for_each_entry(slave, &bus->slaves, node) {
 		if (!slave->dev_num)
 			continue;