[PATCH 1/2] iio: accel: bma180: Fix BMA25x bandwidth register values

[Stephan Gerhold <stephan@gerhold.net>]

According to the BMA253 datasheet [1] and BMA250 datasheet [2] the
bandwidth value for BMA25x should be set as 01xxx:

  "Settings 00xxx result in a bandwidth of 7.81 Hz; [...]
   It is recommended [...] to use the range from ´01000b´ to ´01111b´
   only in order to be compatible with future products."

However, at the moment the drivers sets bandwidth values from 0 to 6,
which is not recommended and always results into 7.81 Hz bandwidth
according to the datasheet.

Fix this by introducing a bw_offset = 8 = 01000b for BMA25x,
so the additional bit is always set for BMA25x.

[1]: https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bma253-ds000.pdf
[2]: https://datasheet.octopart.com/BMA250-Bosch-datasheet-15540103.pdf

Cc: Peter Meerwald <pmeerw@pmeerw.net>
Cc: Linus Walleij <linus.walleij@linaro.org>
Fixes: 2017cff24cc0 ("iio:bma180: Add BMA250 chip support")
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
---
After spending some more time with the driver I noticed that BMA253/BMA254
would actually be better supported by the bmc150-accel driver (which
doesn't have this problem and also supports the motion trigger/interrupt).

I'm preparing a separate patch set to move BMA254 to bmc150-accel at least,
but I'm not sure about BMA250 so this patch is relevant anyway. And I had
it almost done already, so I thought it's better to send it. :)
---
 drivers/iio/accel/bma180.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/accel/bma180.c b/drivers/iio/accel/bma180.c
index 97e991581960..81d1e070a2ee 100644
--- a/drivers/iio/accel/bma180.c
+++ b/drivers/iio/accel/bma180.c
@@ -55,7 +55,7 @@ struct bma180_part_info {
 
 	u8 int_reset_reg, int_reset_mask;
 	u8 sleep_reg, sleep_mask;
-	u8 bw_reg, bw_mask;
+	u8 bw_reg, bw_mask, bw_offset;
 	u8 scale_reg, scale_mask;
 	u8 power_reg, power_mask, lowpower_val;
 	u8 int_enable_reg, int_enable_mask;
@@ -127,6 +127,7 @@ struct bma180_part_info {
 
 #define BMA250_RANGE_MASK	GENMASK(3, 0) /* Range of accel values */
 #define BMA250_BW_MASK		GENMASK(4, 0) /* Accel bandwidth */
+#define BMA250_BW_OFFSET	8
 #define BMA250_SUSPEND_MASK	BIT(7) /* chip will sleep */
 #define BMA250_LOWPOWER_MASK	BIT(6)
 #define BMA250_DATA_INTEN_MASK	BIT(4)
@@ -143,6 +144,7 @@ struct bma180_part_info {
 
 #define BMA254_RANGE_MASK	GENMASK(3, 0) /* Range of accel values */
 #define BMA254_BW_MASK		GENMASK(4, 0) /* Accel bandwidth */
+#define BMA254_BW_OFFSET	8
 #define BMA254_SUSPEND_MASK	BIT(7) /* chip will sleep */
 #define BMA254_LOWPOWER_MASK	BIT(6)
 #define BMA254_DATA_INTEN_MASK	BIT(4)
@@ -287,7 +289,8 @@ static int bma180_set_bw(struct bma180_data *data, int val)
 	for (i = 0; i < data->part_info->num_bw; ++i) {
 		if (data->part_info->bw_table[i] == val) {
 			ret = bma180_set_bits(data, data->part_info->bw_reg,
-				data->part_info->bw_mask, i);
+				data->part_info->bw_mask,
+				i + data->part_info->bw_offset);
 			if (ret) {
 				dev_err(&data->client->dev,
 					"failed to set bandwidth\n");
@@ -880,6 +883,7 @@ static const struct bma180_part_info bma180_part_info[] = {
 		.sleep_mask = BMA250_SUSPEND_MASK,
 		.bw_reg = BMA250_BW_REG,
 		.bw_mask = BMA250_BW_MASK,
+		.bw_offset = BMA250_BW_OFFSET,
 		.scale_reg = BMA250_RANGE_REG,
 		.scale_mask = BMA250_RANGE_MASK,
 		.power_reg = BMA250_POWER_REG,
@@ -909,6 +913,7 @@ static const struct bma180_part_info bma180_part_info[] = {
 		.sleep_mask = BMA254_SUSPEND_MASK,
 		.bw_reg = BMA254_BW_REG,
 		.bw_mask = BMA254_BW_MASK,
+		.bw_offset = BMA254_BW_OFFSET,
 		.scale_reg = BMA254_RANGE_REG,
 		.scale_mask = BMA254_RANGE_MASK,
 		.power_reg = BMA254_POWER_REG,
-- 
2.31.1