[PATCH AUTOSEL for 4.4 056/167] iio: hi8435: avoid garbage event at first enable

Sasha Levin
2018-03-19T17:25:30Z

From: Nikita Yushchenko <nikita.yoush@cogentembedded.com>

[ Upstream commit ee19ac340c5fdfd89c6348be4563453c61ab54a9 ]

Currently, driver generates events for channels if new reading differs
from previous one. This "previous value" is initialized to zero, which
results into event if value is constant-one.

Fix that by initializing "previous value" by reading at event enable
time.

This provides reliable sequence for userspace:
- enable event,
- AFTER THAT read current value,
- AFTER THAT each event will correspond to change.

Signed-off-by: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
drivers/iio/adc/hi8435.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/adc/hi8435.c b/drivers/iio/adc/hi8435.c
index c73c6c62a6ac..ba9e8fc747b8 100644
--- a/drivers/iio/adc/hi8435.c
+++ b/drivers/iio/adc/hi8435.c
@@ -121,10 +121,21 @@ static int hi8435_write_event_config(struct iio_dev *idev,
enum iio_event_direction dir, int state)
{
struct hi8435_priv *priv = iio_priv(idev);
+ int ret;
+ u32 tmp;
+
+ if (state) {
+ ret = hi8435_readl(priv, HI8435_SO31_0_REG, &tmp);
+ if (ret < 0)
+ return ret;
+ if (tmp & BIT(chan->channel))
+ priv->event_prev_val |= BIT(chan->channel);
+ else
+ priv->event_prev_val &= ~BIT(chan->channel);

- priv->event_scan_mask &= ~BIT(chan->channel);
- if (state)
priv->event_scan_mask |= BIT(chan->channel);
+ } else
+ priv->event_scan_mask &= ~BIT(chan->channel);

return 0;
}
--
2.14.1