iio: adc: fsl-imx25-gcq: initialize regulators as needed

The driver tries to initialize all possible regulators from the DT, then
match the external regulators with each channel and then release all unused
regulators.

We can change the logic a bit to initialize regulators only when at least
one channel needs them.

This change creates a mx25_gcq_ext_regulator_setup() function that is
called only for the external regulators. If there's already a reference to
an external regulator, the function will just exit early with no error.

This way, the driver doesn't need to keep any track of these regulators
during init.

Signed-off-by: Alexandru Ardelean <aardelean@deviqon.com>
Link: https://lore.kernel.org/r/20210625074325.9237-1-aardelean@deviqon.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/fsl-imx25-gcq.c

@@ -172,13 +172,35 @@ static const struct regmap_config mx25_gcq_regconfig = {
 	.reg_stride = 4,
 };
 
+static int mx25_gcq_ext_regulator_setup(struct device *dev,
+					struct mx25_gcq_priv *priv, u32 refp)
+{
+	char reg_name[12];
+	int ret;
+
+	if (priv->vref[refp])
+		return 0;
+
+	ret = snprintf(reg_name, sizeof(reg_name), "vref-%s",
+		       mx25_gcq_refp_names[refp]);
+	if (ret < 0)
+		return ret;
+
+	priv->vref[refp] = devm_regulator_get_optional(dev, reg_name);
+	if (IS_ERR(priv->vref[refp]))
+		return dev_err_probe(dev, PTR_ERR(priv->vref[refp]),
+				     "Error, trying to use external voltage reference without a %s regulator.",
+				     reg_name);
+
+	return 0;
+}
+
 static int mx25_gcq_setup_cfgs(struct platform_device *pdev,
 			       struct mx25_gcq_priv *priv)
 {
 	struct device_node *np = pdev->dev.of_node;
 	struct device_node *child;
 	struct device *dev = &pdev->dev;
-	unsigned int refp_used[4] = {};
 	int ret, i;
 
 	/*
@@ -194,19 +216,6 @@ static int mx25_gcq_setup_cfgs(struct platform_device *pdev,
 			     MX25_ADCQ_CFG_IN(i) |
 			     MX25_ADCQ_CFG_REFN_NGND2);
 
-	/*
-	 * First get all regulators to store them in channel_vref_mv if
-	 * necessary. Later we use that information for proper IIO scale
-	 * information.
-	 */
-	priv->vref[MX25_ADC_REFP_INT] = NULL;
-	priv->vref[MX25_ADC_REFP_EXT] =
-		devm_regulator_get_optional(dev, "vref-ext");
-	priv->vref[MX25_ADC_REFP_XP] =
-		devm_regulator_get_optional(dev, "vref-xp");
-	priv->vref[MX25_ADC_REFP_YP] =
-		devm_regulator_get_optional(dev, "vref-yp");
-
 	for_each_child_of_node(np, child) {
 		u32 reg;
 		u32 refp = MX25_ADCQ_CFG_REFP_INT;
@@ -233,11 +242,10 @@ static int mx25_gcq_setup_cfgs(struct platform_device *pdev,
 		case MX25_ADC_REFP_EXT:
 		case MX25_ADC_REFP_XP:
 		case MX25_ADC_REFP_YP:
-			if (IS_ERR(priv->vref[refp])) {
-				dev_err(dev, "Error, trying to use external voltage reference without a vref-%s regulator.",
-					mx25_gcq_refp_names[refp]);
+			ret = mx25_gcq_ext_regulator_setup(&pdev->dev, priv, refp);
+			if (ret) {
 				of_node_put(child);
-				return PTR_ERR(priv->vref[refp]);
+				return ret;
 			}
 			priv->channel_vref_mv[reg] =
 				regulator_get_voltage(priv->vref[refp]);
@@ -253,8 +261,6 @@ static int mx25_gcq_setup_cfgs(struct platform_device *pdev,
 			return -EINVAL;
 		}
 
-		++refp_used[refp];
-
 		/*
 		 * Shift the read values to the correct positions within the
 		 * register.
@@ -285,15 +291,6 @@ static int mx25_gcq_setup_cfgs(struct platform_device *pdev,
 	regmap_write(priv->regs, MX25_ADCQ_CR,
 		     MX25_ADCQ_CR_PDMSK | MX25_ADCQ_CR_QSM_FQS);
 
-	/* Remove unused regulators */
-	for (i = 0; i != 4; ++i) {
-		if (!refp_used[i]) {
-			if (!IS_ERR_OR_NULL(priv->vref[i]))
-				devm_regulator_put(priv->vref[i]);
-			priv->vref[i] = NULL;
-		}
-	}
-
 	return 0;
 }