[PATCH AUTOSEL 3.18 08/13] iio: adc: at91: fix acking DRDY irq on simple conversions

[Sasha Levin <sashal@kernel.org>]

From: Eugen Hristev <eugen.hristev@microchip.com>

[ Upstream commit bc1b45326223e7e890053cf6266357adfa61942d ]

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@bootlin.com>
Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Acked-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/iio/adc/at91_adc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/iio/adc/at91_adc.c b/drivers/iio/adc/at91_adc.c
index 8dc9f442c796..dc438141b75b 100644
--- a/drivers/iio/adc/at91_adc.c
+++ b/drivers/iio/adc/at91_adc.c
@@ -278,6 +278,8 @@ static void handle_adc_eoc_trigger(int irq, struct iio_dev *idev)
 		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);
 	}
-- 
2.17.1