iio: adc: ad799x: add reference voltage capability to chip_info

If the chip supports an external reference voltage
on REFIN pin then the "vref-supply" regulator may be used.

This commit partially refactors 6b104e7895ab16b9b7f466c5f2ca282b87f661e8
to add the capability of the chip to have an external
voltage reference and then remove the ugly conditional check
on chip id.

Suggested-by: Andy Shevchenko <[e-mail]>
Signed-off-by: Stefano Manni <[e-mail]>
Acked-by: Andy Shevchenko <[e-mail]>
Reviewed-by: David Lechner <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/adc/ad799x.c

···
  * @num_channels:	number of channels
  * @noirq_config:	device configuration w/o IRQ
  * @irq_config:		device configuration w/IRQ
+ * @has_vref:		device supports external reference voltage
  */
 struct ad799x_chip_info {
 	int				num_channels;
 	const struct ad799x_chip_config	noirq_config;
 	const struct ad799x_chip_config	irq_config;
+	bool has_vref;
 };
 
 struct ad799x_state {
···
 static const struct ad799x_chip_info ad799x_chip_info_tbl[] = {
 	[ad7991] = {
 		.num_channels = 5,
+		.has_vref = true,
 		.noirq_config = {
 			.channel = {
 				AD799X_CHANNEL(0, 12),
···
 	},
 	[ad7995] = {
 		.num_channels = 5,
+		.has_vref = true,
 		.noirq_config = {
 			.channel = {
 				AD799X_CHANNEL(0, 10),
···
 	},
 	[ad7999] = {
 		.num_channels = 5,
+		.has_vref = true,
 		.noirq_config = {
 			.channel = {
 				AD799X_CHANNEL(0, 8),
···
 		return ret;
 
 	/* check if an external reference is supplied */
-	st->vref = devm_regulator_get_optional(&client->dev, "vref");
-
-	if (IS_ERR(st->vref)) {
-		if (PTR_ERR(st->vref) == -ENODEV) {
+	if (chip_info->has_vref) {
+		st->vref = devm_regulator_get_optional(&client->dev, "vref");
+		ret = PTR_ERR_OR_ZERO(st->vref);
+		if (ret) {
+			if (ret != -ENODEV)
+				goto error_disable_reg;
 			st->vref = NULL;
 			dev_info(&client->dev, "Using VCC reference voltage\n");
-		} else {
-			ret = PTR_ERR(st->vref);
-			goto error_disable_reg;
 		}
-	}
 
-	if (st->vref) {
-		/*
-		 * Use external reference voltage if supported by hardware.
-		 * This is optional if voltage / regulator present, use VCC otherwise.
-		 */
-		if ((st->id == ad7991) || (st->id == ad7995) || (st->id == ad7999)) {
+		if (st->vref) {
 			dev_info(&client->dev, "Using external reference voltage\n");
 			extra_config |= AD7991_REF_SEL;
 			ret = regulator_enable(st->vref);
 			if (ret)
 				goto error_disable_reg;
-		} else {
-			st->vref = NULL;
-			dev_warn(&client->dev, "Supplied reference not supported\n");
 		}
 	}