[PATCH] iio: potentiostat: lmp91000: Handle configuration write errors

[Zhu Jun]

lmp91000_read_config() ignores errors when unlocking and programming
the TIA and reference registers. Probe can then succeed even though
the hardware configuration does not match the parameters used to
interpret measurements.

Check the configuration writes and return the first error. After a
successful unlock, attempt to restore write protection even if a
configuration write fails, and report a relock failure as well.

Fixes: 67e17300dc1d ("iio: potentiostat: add LMP91000 support")
Signed-off-by: Zhu Jun <zhujun2@xxxxxxxxxxxxxxxxxxxx>
---
 drivers/iio/potentiostat/lmp91000.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/drivers/iio/potentiostat/lmp91000.c b/drivers/iio/potentiostat/lmp91000.c
index 00cb3fea97ca..4a29fe627af7 100644
--- a/drivers/iio/potentiostat/lmp91000.c
+++ b/drivers/iio/potentiostat/lmp91000.c
@@ -205,7 +205,7 @@ static int lmp91000_read_config(struct lmp91000_data *data)
 {
 	struct device *dev = data->dev;
 	unsigned int reg, val;
-	int i, ret;
+	int i, ret, lock_ret;
 
 	ret = device_property_read_u32(dev, "ti,tia-gain-ohm", &val);
 	if (ret) {
@@ -250,13 +250,19 @@ static int lmp91000_read_config(struct lmp91000_data *data)
 		return ret;
 	}
 
-	regmap_write(data->regmap, LMP91000_REG_LOCK, 0);
-	regmap_write(data->regmap, LMP91000_REG_TIACN, reg);
-	regmap_write(data->regmap, LMP91000_REG_REFCN,
-		     LMP91000_REG_REFCN_EXT_REF | LMP91000_REG_REFCN_50_ZERO);
-	regmap_write(data->regmap, LMP91000_REG_LOCK, 1);
+	ret = regmap_write(data->regmap, LMP91000_REG_LOCK, 0);
+	if (ret)
+		return ret;
 
-	return 0;
+	ret = regmap_write(data->regmap, LMP91000_REG_TIACN, reg);
+	if (!ret)
+		ret = regmap_write(data->regmap, LMP91000_REG_REFCN,
+				   LMP91000_REG_REFCN_EXT_REF | LMP91000_REG_REFCN_50_ZERO);
+
+	/* Restore write protection even if programming the registers failed. */
+	lock_ret = regmap_write(data->regmap, LMP91000_REG_LOCK, 1);
+
+	return ret ? ret : lock_ret;
 }
 
 static int lmp91000_buffer_cb(const void *val, void *private)
-- 
2.51.0