iio: adc: at91-sama5d2_adc: fix differential channels in triggered mode

The differential channels require writing the channel offset register (COR).
Otherwise they do not work in differential mode.
The configuration of COR is missing in triggered mode.

Fixes: 5e1a1da0 ("iio: adc: at91-sama5d2_adc: add hw trigger and buffer support")
Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/at91-sama5d2_adc.c

@@ -723,6 +723,7 @@ static int at91_adc_configure_trigger(struct iio_trigger *trig, bool state)
 
 	for_each_set_bit(bit, indio->active_scan_mask, indio->num_channels) {
 		struct iio_chan_spec const *chan = at91_adc_chan_get(indio, bit);
+		u32 cor;
 
 		if (!chan)
 			continue;
@@ -731,6 +732,20 @@ static int at91_adc_configure_trigger(struct iio_trigger *trig, bool state)
 		    chan->type == IIO_PRESSURE)
 			continue;
 
+		if (state) {
+			cor = at91_adc_readl(st, AT91_SAMA5D2_COR);
+
+			if (chan->differential)
+				cor |= (BIT(chan->channel) |
+					BIT(chan->channel2)) <<
+					AT91_SAMA5D2_COR_DIFF_OFFSET;
+			else
+				cor &= ~(BIT(chan->channel) <<
+				       AT91_SAMA5D2_COR_DIFF_OFFSET);
+
+			at91_adc_writel(st, AT91_SAMA5D2_COR, cor);
+		}
+
 		if (state) {
 			at91_adc_writel(st, AT91_SAMA5D2_CHER,
 					BIT(chan->channel));