iio: adc: stm32-adc: dma transfers cleanup

- Remove processing related to DMA in irq handler as this
data transfer is managed directly in DMA callback.
- Update comment in stm32_adc_set_watermark() function.
Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
Reviewed-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Link: https://lore.kernel.org/r/20201105142941.27301-1-olivier.moysan@st.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/stm32-adc.c

@@ -1310,7 +1310,7 @@ static int stm32_adc_set_watermark(struct iio_dev *indio_dev, unsigned int val)
 	 * dma cyclic transfers are used, buffer is split into two periods.
 	 * There should be :
 	 * - always one buffer (period) dma is working on
-	 * - one buffer (period) driver can push with iio_trigger_poll().
+	 * - one buffer (period) driver can push data.
 	 */
 	watermark = min(watermark, val * (unsigned)(sizeof(u16)));
 	adc->rx_buf_sz = min(rx_buf_sz, watermark * 2 * adc->num_conv);
@@ -1573,30 +1573,13 @@ static irqreturn_t stm32_adc_trigger_handler(int irq, void *p)
 
 	dev_dbg(&indio_dev->dev, "%s bufi=%d\n", __func__, adc->bufi);
 
-	if (!adc->dma_chan) {
 	/* reset buffer index */
 	adc->bufi = 0;
 	iio_push_to_buffers_with_timestamp(indio_dev, adc->buffer,
 					   pf->timestamp);
-	} else {
-		int residue = stm32_adc_dma_residue(adc);
-
-		while (residue >= indio_dev->scan_bytes) {
-			u16 *buffer = (u16 *)&adc->rx_buf[adc->bufi];
-
-			iio_push_to_buffers_with_timestamp(indio_dev, buffer,
-							   pf->timestamp);
-			residue -= indio_dev->scan_bytes;
-			adc->bufi += indio_dev->scan_bytes;
-			if (adc->bufi >= adc->rx_buf_sz)
-				adc->bufi = 0;
-		}
-	}
-
 	iio_trigger_notify_done(indio_dev->trig);
 
 	/* re-enable eoc irq */
-	if (!adc->dma_chan)
 	stm32_adc_conv_irq_enable(adc);
 
 	return IRQ_HANDLED;