[PATCH 3.19.y-ckt 023/146] iio: adc: xilinx: Fix VREFN sign

[Kamal Mostafa]

3.19.8-ckt2 -stable review patch.  If anyone has any objections, please let me know.

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

From: Thomas Betker <thomas.betker at rohde-schwarz.com>

commit 97ffae1d30c3f6ceee67d5b0d3e540c08c13c744 upstream.

The VREFN channel is bipolar, not unipolar. Small negative values do
occur (e.g., -1mV), and unsigned conversion maps them incorrectly to
large positive values (about +1V), so fix this.

Signed-off-by: Thomas Betker <thomas.betker at rohde-schwarz.com>
Signed-off-by: Jonathan Cameron <jic23 at kernel.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/iio/adc/xilinx-xadc-core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iio/adc/xilinx-xadc-core.c b/drivers/iio/adc/xilinx-xadc-core.c
index 6fa629b..ce93bd8 100644
--- a/drivers/iio/adc/xilinx-xadc-core.c
+++ b/drivers/iio/adc/xilinx-xadc-core.c
@@ -997,7 +997,7 @@ static const struct iio_event_spec xadc_voltage_events[] = {
 	.num_event_specs = (_alarm) ? ARRAY_SIZE(xadc_voltage_events) : 0, \
 	.scan_index = (_scan_index), \
 	.scan_type = { \
-		.sign = 'u', \
+		.sign = ((_addr) == XADC_REG_VREFN) ? 's' : 'u', \
 		.realbits = 12, \
 		.storagebits = 16, \
 		.shift = 4, \
-- 
1.9.1