hwmon: (tmp421) really disable channels

Recent patch added possibility to disable selected channels. That would
only make sure that the ENODATA is returned for those channels but would
not configure the actual hardware.

With this patch, the config register is written to make sure the
channels are disabled also at hardware level.

Signed-off-by: Krzysztof Adamski <krzysztof.adamski@nokia.com>

drivers/hwmon/tmp421.c

@@ -33,6 +33,8 @@ enum chips { tmp421, tmp422, tmp423, tmp441, tmp442 };
 /* The TMP421 registers */
 #define TMP421_STATUS_REG			0x08
 #define TMP421_CONFIG_REG_1			0x09
+#define TMP421_CONFIG_REG_2			0x0A
+#define TMP421_CONFIG_REG_REN(x)		(BIT(3 + (x)))
 #define TMP421_CONVERSION_RATE_REG		0x0B
 #define TMP421_N_FACTOR_REG_1			0x21
 #define TMP421_MANUFACTURER_ID_REG		0xFE
@@ -351,6 +353,25 @@ void tmp421_probe_from_dt(struct i2c_client *client, struct tmp421_data *data)
 	}
 }
 
+void tmp421_disable_channels(struct i2c_client *client, uint8_t mask)
+{
+	int err;
+	int cfg = i2c_smbus_read_byte_data(client, TMP421_CONFIG_REG_2);
+
+	if (cfg < 0) {
+		dev_err(&client->dev,
+			"error reading register, can't disable channels\n");
+		return;
+	}
+
+	cfg &= ~mask;
+
+	err = i2c_smbus_write_byte_data(client, TMP421_CONFIG_REG_2, cfg);
+	if (err < 0)
+		dev_err(&client->dev,
+			"error writing register, can't disable channels\n");
+}
+
 static const struct hwmon_ops tmp421_ops = {
 	.is_visible = tmp421_is_visible,
 	.read = tmp421_read,
@@ -363,6 +384,7 @@ static int tmp421_probe(struct i2c_client *client)
 	struct device *hwmon_dev;
 	struct tmp421_data *data;
 	int i, err;
+	u8 disable = 0;
 
 	data = devm_kzalloc(dev, sizeof(struct tmp421_data), GFP_KERNEL);
 	if (!data)
@@ -380,11 +402,18 @@ static int tmp421_probe(struct i2c_client *client)
 	if (err)
 		return err;
 
-	for (i = 0; i < data->channels; i++)
-		data->temp_config[i] = HWMON_T_INPUT | HWMON_T_FAULT;
-
 	tmp421_probe_from_dt(client, data);
 
+	for (i = 0; i < data->channels; i++) {
+		data->temp_config[i] |= HWMON_T_INPUT | HWMON_T_FAULT;
+		if (data->channel[i].disabled)
+			disable |= TMP421_CONFIG_REG_REN(i);
+
+	}
+
+	if (disable)
+		tmp421_disable_channels(client, disable);
+
 	data->chip.ops = &tmp421_ops;
 	data->chip.info = data->info;