iio: at91-sama5d2_adc: adjust iio_triggered_buffer_{predisable,postenable} positions

The iio_triggered_buffer_{predisable,postenable} functions attach/detach
poll functions.

In most cases the iio_triggered_buffer_postenable() should be called first
to attach the poll function, and then the driver can init the data to be
triggered.
In this case it's the other way around: the DMA code should be initialized
before the attaching the poll function and the reverse should be done when
un-initializing.

To make things easier when removing the iio_triggered_buffer_postenable() &
iio_triggered_buffer_predisable() functions from the IIO core API, the DMA
code has been moved into preenable() for init, and postdisable() for
uninit.
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Reviewed-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Reviewed-by: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/at91-sama5d2_adc.c

@@ -883,7 +883,7 @@ static bool at91_adc_current_chan_is_touch(struct iio_dev *indio_dev)
 			       AT91_SAMA5D2_MAX_CHAN_IDX + 1);
 }
 
-static int at91_adc_buffer_postenable(struct iio_dev *indio_dev)
+static int at91_adc_buffer_preenable(struct iio_dev *indio_dev)
 {
 	int ret;
 	u8 bit;
@@ -934,13 +934,20 @@ static int at91_adc_buffer_postenable(struct iio_dev *indio_dev)
 	if (at91_adc_buffer_check_use_irq(indio_dev, st))
 		at91_adc_writel(st, AT91_SAMA5D2_IER, AT91_SAMA5D2_IER_DRDY);
 
+	return 0;
+}
+
+static int at91_adc_buffer_postenable(struct iio_dev *indio_dev)
+{
+	if (at91_adc_current_chan_is_touch(indio_dev))
+		return 0;
+
 	return iio_triggered_buffer_postenable(indio_dev);
 }
 
-static int at91_adc_buffer_predisable(struct iio_dev *indio_dev)
+static int at91_adc_buffer_postdisable(struct iio_dev *indio_dev)
 {
 	struct at91_adc_state *st = iio_priv(indio_dev);
-	int ret;
 	u8 bit;
 
 	/* check if we are disabling triggered buffer or the touchscreen */
@@ -981,19 +988,24 @@ static int at91_adc_buffer_predisable(struct iio_dev *indio_dev)
 	/* read overflow register to clear possible overflow status */
 	at91_adc_readl(st, AT91_SAMA5D2_OVER);
 
-	/* continue with the triggered buffer */
-	ret = iio_triggered_buffer_predisable(indio_dev);
-	if (ret < 0)
-		dev_err(&indio_dev->dev, "buffer predisable failed\n");
-
 	/* if we are using DMA we must clear registers and end DMA */
 	if (st->dma_st.dma_chan)
 		dmaengine_terminate_sync(st->dma_st.dma_chan);
 
-	return ret;
+	return 0;
+}
+
+static int at91_adc_buffer_predisable(struct iio_dev *indio_dev)
+{
+	if (at91_adc_current_chan_is_touch(indio_dev))
+		return 0;
+
+	return iio_triggered_buffer_predisable(indio_dev);
 }
 
 static const struct iio_buffer_setup_ops at91_buffer_setup_ops = {
+	.preenable = &at91_adc_buffer_preenable,
+	.postdisable = &at91_adc_buffer_postdisable,
 	.postenable = &at91_adc_buffer_postenable,
 	.predisable = &at91_adc_buffer_predisable,
 };