i2c: mux: pca954x: Track unknown mux state and report deselect failures

index 8fca709ed279..e34b4668a1fa 100644
@@ -107,7 +107,7 @@ struct chip_desc {
 struct pca954x {
 	const struct chip_desc *chip;
 
-	u8 last_chan;		/* last register value */
+	s16 last_chan;		/* last register value, or -1 if unknown */
 	/* MUX_IDLE_AS_IS, MUX_IDLE_DISCONNECT or >= 0 for channel */
 	s32 idle_state;
 

@@ -327,7 +327,7 @@ static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
 	/* Only select the channel if its different from the last channel */
 	if (data->last_chan != regval) {
 		ret = pca954x_reg_write(muxc->parent, client, regval);
-		data->last_chan = ret < 0 ? 0 : regval;
+		data->last_chan = ret < 0 ? -1 : regval;
 	}
 
 	return ret;

@@ -338,6 +338,7 @@ static int pca954x_deselect_mux(struct i2c_mux_core *muxc, u32 chan)
 	struct pca954x *data = i2c_mux_priv(muxc);
 	struct i2c_client *client = data->client;
 	s32 idle_state;
+	int ret;
 
 	idle_state = READ_ONCE(data->idle_state);
 	if (idle_state >= 0)

@@ -346,9 +347,9 @@ static int pca954x_deselect_mux(struct i2c_mux_core *muxc, u32 chan)
 
 	if (idle_state == MUX_IDLE_DISCONNECT) {
 		/* Deselect active channel */
-		data->last_chan = 0;
-		return pca954x_reg_write(muxc->parent, client,
-					 data->last_chan);
+		ret = pca954x_reg_write(muxc->parent, client, 0);
+		data->last_chan = ret < 0 ? -1 : 0;
+		return ret;
 	}
 
 	/* otherwise leave as-is */

@@ -392,7 +393,7 @@ static ssize_t idle_state_store(struct device *dev,
 	 * Set the mux into a state consistent with the new
 	 * idle_state.
 	 */
-	if (data->last_chan || val != MUX_IDLE_DISCONNECT)
+	if (data->last_chan != 0 || val != MUX_IDLE_DISCONNECT)
 		ret = pca954x_deselect_mux(muxc, 0);
 
 	i2c_unlock_bus(muxc->parent, I2C_LOCK_SEGMENT);

@@ -480,12 +481,13 @@ static void pca954x_cleanup(struct i2c_mux_core *muxc)
 
 static int pca954x_init(struct i2c_client *client, struct pca954x *data)
 {
+	u8 regval;
 	int ret;
 
 	if (data->idle_state >= 0)
-		data->last_chan = pca954x_regval(data, data->idle_state);
+		regval = pca954x_regval(data, data->idle_state);
 	else
-		data->last_chan = 0; /* Disconnect multiplexer */
+		regval = 0; /* Disconnect multiplexer */
 
 	if (device_is_compatible(&client->dev, "maxim,max7357")) {
 		if (i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_WRITE_BYTE_DATA)) {

@@ -505,18 +507,17 @@ static int pca954x_init(struct i2c_client *client, struct pca954x *data)
 						      "maxim,preconnection-wiggle-test-enable"))
 				conf |= MAX7357_CONF_PRECONNECT_TEST;
 
-			ret = i2c_smbus_write_byte_data(client, data->last_chan, conf);
+			ret = i2c_smbus_write_byte_data(client, regval, conf);
 		} else {
 			dev_warn(&client->dev, "Write byte data not supported."
 				 "Cannot enable enhanced mode features\n");
-			ret = i2c_smbus_write_byte(client, data->last_chan);
+			ret = i2c_smbus_write_byte(client, regval);
 		}
 	} else {
-		ret = i2c_smbus_write_byte(client, data->last_chan);
+		ret = i2c_smbus_write_byte(client, regval);
 	}
 
-	if (ret < 0)
-		data->last_chan = 0;
+	data->last_chan = ret < 0 ? -1 : regval;
 
 	return ret;
 }

index e34b4668a1fa..91df2d2fa2b7 100644
@@ -333,7 +333,8 @@ static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
 	return ret;
 }
 
-static int pca954x_deselect_mux(struct i2c_mux_core *muxc, u32 chan)
+/* Program the mux into the state that corresponds to idle_state. */
+static int pca954x_set_idle_state(struct i2c_mux_core *muxc)
 {
 	struct pca954x *data = i2c_mux_priv(muxc);
 	struct i2c_client *client = data->client;

@@ -345,16 +346,20 @@ static int pca954x_deselect_mux(struct i2c_mux_core *muxc, u32 chan)
 		/* Set the mux back to a predetermined channel */
 		return pca954x_select_chan(muxc, idle_state);
 
-	if (idle_state == MUX_IDLE_DISCONNECT) {
-		/* Deselect active channel */
-		ret = pca954x_reg_write(muxc->parent, client, 0);
-		data->last_chan = ret < 0 ? -1 : 0;
-		return ret;
-	}
+	/* Leave the mux as-is unless idle_state is MUX_IDLE_DISCONNECT */
+	if (idle_state != MUX_IDLE_DISCONNECT)
+		return 0;
 
-	/* otherwise leave as-is */
+	/* Deselect active channel */
+	ret = pca954x_reg_write(muxc->parent, client, 0);
+	data->last_chan = ret < 0 ? -1 : 0;
 
-	return 0;
+	return ret;
+}
+
+static int pca954x_deselect_mux(struct i2c_mux_core *muxc, u32 chan)
+{
+	return pca954x_set_idle_state(muxc);
 }
 
 static ssize_t idle_state_show(struct device *dev,

@@ -394,7 +399,7 @@ static ssize_t idle_state_store(struct device *dev,
 	 * idle_state.
 	 */
 	if (data->last_chan != 0 || val != MUX_IDLE_DISCONNECT)
-		ret = pca954x_deselect_mux(muxc, 0);
+		ret = pca954x_set_idle_state(muxc);
 
 	i2c_unlock_bus(muxc->parent, I2C_LOCK_SEGMENT);
 

index 91df2d2fa2b7..45a7d841e7cf 100644
@@ -359,7 +359,21 @@ static int pca954x_set_idle_state(struct i2c_mux_core *muxc)
 
 static int pca954x_deselect_mux(struct i2c_mux_core *muxc, u32 chan)
 {
-	return pca954x_set_idle_state(muxc);
+	struct pca954x *data = i2c_mux_priv(muxc);
+	int ret;
+
+	ret = pca954x_set_idle_state(muxc);
+	/*
+	 * The i2c-mux core ignores the deselect return value. Report failures
+	 * since these may leave a channel connected until the next transfer
+	 * reprograms the mux.
+	 */
+	if (ret < 0)
+		dev_warn_ratelimited(&data->client->dev,
+				     "failed to deselect channel %u: %d\n",
+				     chan, ret);
+
+	return ret;
 }
 
 static ssize_t idle_state_show(struct device *dev,