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Subject[PATCH 4.4 055/190] iio: hi8435: avoid garbage event at first enable
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

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

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/iio/adc/hi8435.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)

--- a/drivers/iio/adc/hi8435.c
+++ b/drivers/iio/adc/hi8435.c
@@ -121,10 +121,21 @@ static int hi8435_write_event_config(str
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;
}

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