iio: adc: max1027: Don't reject external triggers when there is no IRQ

External triggers do not necessarily need the EOC interrupt to be
populated to work properly. The end of conversion status may either come
from an interrupt or from a sufficient enough extra delay. IRQs are not
mandatory so move the triggered buffer setup out of the IRQ condition
and add the logic to wait enough time for all the requested conversions
to be in the device's FIFO.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20210921115408.66711-17-miquel.raynal@bootlin.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/max1027.c

@@ -289,6 +289,9 @@ static int max1027_wait_eoc(struct iio_dev *indio_dev)
 		if (!ret)
 			return ret;
 	} else {
+		if (indio_dev->active_scan_mask)
+			conversion_time *= hweight32(*indio_dev->active_scan_mask);
+
 		usleep_range(conversion_time, conversion_time * 2);
 	}
 
@@ -568,16 +571,18 @@ static int max1027_probe(struct spi_device *spi)
 	if (!st->buffer)
 		return -ENOMEM;
 
-	if (spi->irq) {
-		ret = devm_iio_triggered_buffer_setup(&spi->dev, indio_dev,
-						      &iio_pollfunc_store_time,
-						      &max1027_trigger_handler,
-						      NULL);
-		if (ret < 0) {
-			dev_err(&indio_dev->dev, "Failed to setup buffer\n");
-			return ret;
-		}
+	/* Enable triggered buffers */
+	ret = devm_iio_triggered_buffer_setup(&spi->dev, indio_dev,
+					      &iio_pollfunc_store_time,
+					      &max1027_trigger_handler,
+					      NULL);
+	if (ret < 0) {
+		dev_err(&indio_dev->dev, "Failed to setup buffer\n");
+		return ret;
+	}
 
+	/* If there is an EOC interrupt, register the cnvst hardware trigger */
+	if (spi->irq) {
 		st->trig = devm_iio_trigger_alloc(&spi->dev, "%s-trigger",
 						  indio_dev->name);
 		if (!st->trig) {