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From:   Jagath Jog J <jagathjog1996@gmail.com>
To:     dan@dlrobertson.com, jic23@kernel.org, andy.shevchenko@gmail.com
Cc:     linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v5 01/10] iio: accel: bma400: Fix the scale min and max macro values
Date:   Thu,  5 May 2022 19:00:12 +0530
Message-Id: <20220505133021.22362-2-jagathjog1996@gmail.com>
In-Reply-To: <20220505133021.22362-1-jagathjog1996@gmail.com>
References: <20220505133021.22362-1-jagathjog1996@gmail.com>
Precedence: bulk

Changing the scale macro values to match the bma400 sensitivity
for 1 LSB of all the available ranges.

Fixes: 465c811f1f20 ("iio: accel: Add driver for the BMA400")
Signed-off-by: Jagath Jog J <jagathjog1996@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
---
 drivers/iio/accel/bma400.h | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/accel/bma400.h b/drivers/iio/accel/bma400.h
index c4c8d74155c2..80330c7ce17f 100644
--- a/drivers/iio/accel/bma400.h
+++ b/drivers/iio/accel/bma400.h
@@ -83,8 +83,27 @@
 #define BMA400_ACC_ODR_MIN_WHOLE_HZ 25
 #define BMA400_ACC_ODR_MIN_HZ       12
 
-#define BMA400_SCALE_MIN            38357
-#define BMA400_SCALE_MAX            306864
+/*
+ * BMA400_SCALE_MIN macro value represents m/s^2 for 1 LSB before
+ * converting to micro values for +-2g range.
+ *
+ * For +-2g - 1 LSB = 0.976562 milli g = 0.009576 m/s^2
+ * For +-4g - 1 LSB = 1.953125 milli g = 0.019153 m/s^2
+ * For +-16g - 1 LSB = 7.8125 milli g = 0.076614 m/s^2
+ *
+ * The raw value which is used to select the different ranges is determined
+ * by the first bit set position from the scale value, so BMA400_SCALE_MIN
+ * should be odd.
+ *
+ * Scale values for +-2g, +-4g, +-8g and +-16g are populated into bma400_scales
+ * array by left shifting BMA400_SCALE_MIN.
+ * e.g.:
+ * To select +-2g = 9577 << 0 = raw value to write is 0.
+ * To select +-8g = 9577 << 2 = raw value to write is 2.
+ * To select +-16g = 9577 << 3 = raw value to write is 3.
+ */
+#define BMA400_SCALE_MIN            9577
+#define BMA400_SCALE_MAX            76617
 
 #define BMA400_NUM_REGULATORS       2
 #define BMA400_VDD_REGULATOR        0
-- 
2.17.1