[PATCH 4.19 260/361] iio: adc: at91: fix acking DRDY irq on simple conversions

[Greg Kroah-Hartman]

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eugen Hristev <eugen.hristev@xxxxxxxxxxxxx>

commit bc1b45326223e7e890053cf6266357adfa61942d upstream.

When doing simple conversions, the driver did not acknowledge the DRDY irq.
If this irq status is not acked, it will be left pending, and as soon as a
trigger is enabled, the irq handler will be called, it doesn't know why
this status has occurred because no channel is pending, and then it will go
int a irq loop and board will hang.
To avoid this situation, read the LCDR after a raw conversion is done.

Fixes: 0e589d5fb ("ARM: AT91: IIO: Add AT91 ADC driver.")
Cc: Maxime Ripard <maxime.ripard@xxxxxxxxxxx>
Signed-off-by: Eugen Hristev <eugen.hristev@xxxxxxxxxxxxx>
Acked-by: Ludovic Desroches <ludovic.desroches@xxxxxxxxxxxxx>
Cc: <Stable@xxxxxxxxxxxxxxx>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/iio/adc/at91_adc.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/iio/adc/at91_adc.c
+++ b/drivers/iio/adc/at91_adc.c
@@ -279,6 +279,8 @@ static void handle_adc_eoc_trigger(int i
 		iio_trigger_poll(idev->trig);
 	} else {
 		st->last_value = at91_adc_readl(st, AT91_ADC_CHAN(st, st->chnb));
+		/* Needed to ACK the DRDY interruption */
+		at91_adc_readl(st, AT91_ADC_LCDR);
 		st->done = true;
 		wake_up_interruptible(&st->wq_data_avail);
 	}