iio: adc: ti-ads1015: write config register only on change

There is no point writing ADS1015_CFG_REG when configuration
didn't change. Avoid that.

Cc: Daniel Baluta <daniel.baluta@gmail.com>
Cc: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
Reviewed-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ti-ads1015.c

@@ -332,7 +332,7 @@ static int ads1015_set_power_state(struct ads1015_data *data, bool on)
 static
 int ads1015_get_adc_result(struct ads1015_data *data, int chan, int *val)
 {
-	int ret, pga, dr, conv_time;
+	int ret, pga, dr, dr_old, conv_time;
 	unsigned int old, mask, cfg;
 
 	if (chan < 0 || chan >= ADS1015_CHANNELS)
@@ -358,15 +358,14 @@ int ads1015_get_adc_result(struct ads1015_data *data, int chan, int *val)
 	}
 
 	cfg = (old & ~mask) | (cfg & mask);
-
-	ret = regmap_write(data->regmap, ADS1015_CFG_REG, cfg);
-	if (ret)
-		return ret;
-
-	if (old != cfg || data->conv_invalid) {
-		int dr_old = (old & ADS1015_CFG_DR_MASK) >>
-				ADS1015_CFG_DR_SHIFT;
-
+	if (old != cfg) {
+		ret = regmap_write(data->regmap, ADS1015_CFG_REG, cfg);
+		if (ret)
+			return ret;
+		data->conv_invalid = true;
+	}
+	if (data->conv_invalid) {
+		dr_old = (old & ADS1015_CFG_DR_MASK) >> ADS1015_CFG_DR_SHIFT;
 		conv_time = DIV_ROUND_UP(USEC_PER_SEC, data->data_rate[dr_old]);
 		conv_time += DIV_ROUND_UP(USEC_PER_SEC, data->data_rate[dr]);
 		usleep_range(conv_time, conv_time + 1);