iio: adc: rockchip_saradc: add voltage notifier so get referenced voltage once at probe

Add voltage notifier, no need to query regulator voltage for
every saradc read, just get regulator voltage once at probe.
Signed-off-by: David Wu <david.wu@rock-chips.com>
Signed-off-by: Simon Xue <xxm@rock-chips.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20210810011007.54066-1-xxm@rock-chips.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/rockchip_saradc.c

@@ -49,10 +49,12 @@ struct rockchip_saradc {
 	struct clk		*clk;
 	struct completion	completion;
 	struct regulator	*vref;
+	int			uv_vref;
 	struct reset_control	*reset;
 	const struct rockchip_saradc_data *data;
 	u16			last_val;
 	const struct iio_chan_spec *last_chan;
+	struct notifier_block nb;
 };
 
 static void rockchip_saradc_power_down(struct rockchip_saradc *info)
@@ -105,13 +107,7 @@ static int rockchip_saradc_read_raw(struct iio_dev *indio_dev,
 		mutex_unlock(&indio_dev->mlock);
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_SCALE:
-		ret = regulator_get_voltage(info->vref);
-		if (ret < 0) {
-			dev_err(&indio_dev->dev, "failed to get voltage\n");
-			return ret;
-		}
-
-		*val = ret / 1000;
+		*val = info->uv_vref / 1000;
 		*val2 = chan->scan_type.realbits;
 		return IIO_VAL_FRACTIONAL_LOG2;
 	default:
@@ -298,6 +294,26 @@ static irqreturn_t rockchip_saradc_trigger_handler(int irq, void *p)
 	return IRQ_HANDLED;
 }
 
+static int rockchip_saradc_volt_notify(struct notifier_block *nb,
+						   unsigned long event,
+						   void *data)
+{
+	struct rockchip_saradc *info =
+			container_of(nb, struct rockchip_saradc, nb);
+
+	if (event & REGULATOR_EVENT_VOLTAGE_CHANGE)
+		info->uv_vref = (unsigned long)data;
+
+	return NOTIFY_OK;
+}
+
+static void rockchip_saradc_regulator_unreg_notifier(void *data)
+{
+	struct rockchip_saradc *info = data;
+
+	regulator_unregister_notifier(info->vref, &info->nb);
+}
+
 static int rockchip_saradc_probe(struct platform_device *pdev)
 {
 	struct rockchip_saradc *info = NULL;
@@ -410,6 +426,12 @@ static int rockchip_saradc_probe(struct platform_device *pdev)
 		return ret;
 	}
 
+	ret = regulator_get_voltage(info->vref);
+	if (ret < 0)
+		return ret;
+
+	info->uv_vref = ret;
+
 	ret = clk_prepare_enable(info->pclk);
 	if (ret < 0) {
 		dev_err(&pdev->dev, "failed to enable pclk\n");
@@ -450,6 +472,17 @@ static int rockchip_saradc_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
+	info->nb.notifier_call = rockchip_saradc_volt_notify;
+	ret = regulator_register_notifier(info->vref, &info->nb);
+	if (ret)
+		return ret;
+
+	ret = devm_add_action_or_reset(&pdev->dev,
+				       rockchip_saradc_regulator_unreg_notifier,
+				       info);
+	if (ret)
+		return ret;
+
 	return devm_iio_device_register(&pdev->dev, indio_dev);
 }