iio: adc: at91-sama5d2_adc: exit from write_raw() when buffers are enabled

When buffers are enabled conversion may start asynchronously thus
allowing changes on actual hardware could lead to bad behavior. Thus
do not allow changing oversampling ratio and sample frequency when
buffers are enabled.

Fixes: 5e1a1da ("iio: adc: at91-sama5d2_adc: add hw trigger and buffer support")
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>

Author: claudiubeznea

drivers/iio/adc/at91-sama5d2_adc.c

@@ -1683,6 +1683,9 @@ static int at91_adc_write_raw(struct iio_dev *indio_dev,
 	struct at91_adc_state *st = iio_priv(indio_dev);
 	int ret = 0;
 
+	if (iio_buffer_enabled(indio_dev))
+		return -EBUSY;
+
 	switch (mask) {
 	case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
 		if ((val != AT91_OSR_1SAMPLES) && (val != AT91_OSR_4SAMPLES) &&