iio: mxs-lradc: only update the buffer when its conversions have finished

commit 89bb35e2 upstream.

Using the touchscreen while running buffered capture results in the
buffer reporting lots of wrong values, often just zeros. This is because
we push readings to the buffer every time a touchscreen interrupt
arrives, including when the buffer's own conversions have not yet
finished. So let's only push to the buffer when its conversions are
ready.
Signed-off-by: Kristina Martšenko <kristina.martsenko@gmail.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/staging/iio/adc/mxs-lradc.c

@@ -1157,10 +1157,12 @@ static irqreturn_t mxs_lradc_handle_irq(int irq, void *data)
 				LRADC_CTRL1_LRADC_IRQ(TOUCHSCREEN_VCHANNEL2));
 	}
 
-	if (iio_buffer_enabled(iio))
-		iio_trigger_poll(iio->trig, iio_get_time_ns());
-	else if (reg & LRADC_CTRL1_LRADC_IRQ(0))
+	if (iio_buffer_enabled(iio)) {
+		if (reg & lradc->buffer_vchans)
+			iio_trigger_poll(iio->trig, iio_get_time_ns());
+	} else if (reg & LRADC_CTRL1_LRADC_IRQ(0)) {
 		complete(&lradc->completion);
+	}
 
 	mxs_lradc_reg_clear(lradc, reg & clr_irq, LRADC_CTRL1);