[PATCH v2] iio: bu27034: Ensure reset is written

[Matti Vaittinen <mazziesaccount@gmail.com>]

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The reset bit must be always written to the hardware no matter what value
is in a cache or register. Ensure this by using regmap_write_bits()
instead of the regmap_update_bits(). Furthermore, the RESET bit may be
self-clearing, so mark the SYSTEM_CONTROL register volatile to guarantee
we do also read the right state - should we ever need to read it.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
Fixes: e52afbd61039 ("iio: light: ROHM BU27034 Ambient Light Sensor")

---
Changelog:
v1 => v2:
  - Fix SoB tag


I haven't verified if the reset bit is self-clearin as I did temporarily
give away the HW.

In worst case the bit is not self clearing - but we don't really
get performance penalty even if we set the register volatile because the
SYSTEM_CONTROL register only has the part-ID and the reset fields. The
part-id is only read once at probe.

---
 drivers/iio/light/rohm-bu27034.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/light/rohm-bu27034.c b/drivers/iio/light/rohm-bu27034.c
index 25c9b79574a5..740ebd86b6e5 100644
--- a/drivers/iio/light/rohm-bu27034.c
+++ b/drivers/iio/light/rohm-bu27034.c
@@ -231,6 +231,9 @@ struct bu27034_result {
 
 static const struct regmap_range bu27034_volatile_ranges[] = {
 	{
+		.range_min = BU27034_REG_SYSTEM_CONTROL,
+		.range_max = BU27034_REG_SYSTEM_CONTROL,
+	}, {
 		.range_min = BU27034_REG_MODE_CONTROL4,
 		.range_max = BU27034_REG_MODE_CONTROL4,
 	}, {
@@ -1272,7 +1275,7 @@ static int bu27034_chip_init(struct bu27034_data *data)
 	int ret, sel;
 
 	/* Reset */
-	ret = regmap_update_bits(data->regmap, BU27034_REG_SYSTEM_CONTROL,
+	ret = regmap_write_bits(data->regmap, BU27034_REG_SYSTEM_CONTROL,
 			   BU27034_MASK_SW_RESET, BU27034_MASK_SW_RESET);
 	if (ret)
 		return dev_err_probe(data->dev, ret, "Sensor reset failed\n");

base-commit: 7fcbd72176076c44b47e8f68f0223c02c411f420
-- 
2.40.0


-- 
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =] 

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