[PATCH v3 08/11] iio: light: cm32181: Use units of 1/100000th for calibscale and lux_per_bit

Hans de Goede
2020-04-28T17:30:03Z

Use units of 1/100000th for calibscale and lux_per_bit. The similar
cm3232 driver already uses 1/100000th as unit for calibscale.

This allows for higher-accuracy and makes it easier to add support
for getting device-specific calibscale and lux_per_bit values from
a device's ACPI tables, as the values in the ACPI tables also use
1/100000th units.

This units change means that our intermediate values in cm32181_get_lux()
may get quite big, change the type of the lux variable to a u64 to
deal with this.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
drivers/iio/light/cm32181.c | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/drivers/iio/light/cm32181.c b/drivers/iio/light/cm32181.c
index bcea669d20cb..1ad7d4582d1c 100644
--- a/drivers/iio/light/cm32181.c
+++ b/drivers/iio/light/cm32181.c
@@ -45,11 +45,11 @@
#define CM32181_CMD_ALS_SM_MASK (0x03 << CM32181_CMD_ALS_SM_SHIFT)
#define CM32181_CMD_ALS_SM_DEFAULT (0x01 << CM32181_CMD_ALS_SM_SHIFT)

-#define CM32181_MLUX_PER_BIT 5 /* ALS_SM=01 IT=800ms */
-#define CM32181_MLUX_PER_BIT_BASE_IT 800000 /* Based on IT=800ms */
-#define CM32181_CALIBSCALE_DEFAULT 1000
-#define CM32181_CALIBSCALE_RESOLUTION 1000
-#define MLUX_PER_LUX 1000
+#define CM32181_LUX_PER_BIT 500 /* ALS_SM=01 IT=800ms */
+#define CM32181_LUX_PER_BIT_RESOLUTION 100000
+#define CM32181_LUX_PER_BIT_BASE_IT 800000 /* Based on IT=800ms */
+#define CM32181_CALIBSCALE_DEFAULT 100000
+#define CM32181_CALIBSCALE_RESOLUTION 100000

#define SMBUS_ALERT_RESPONSE_ADDRESS 0x0c

@@ -204,15 +204,15 @@ static int cm32181_get_lux(struct cm32181_chip *cm32181)
struct i2c_client *client = cm32181->client;
int ret;
int als_it;
- unsigned long lux;
+ u64 lux;

ret = cm32181_read_als_it(cm32181, &als_it);
if (ret < 0)
return -EINVAL;

- lux = CM32181_MLUX_PER_BIT;
- lux *= CM32181_MLUX_PER_BIT_BASE_IT;
- lux /= als_it;
+ lux = CM32181_LUX_PER_BIT;
+ lux *= CM32181_LUX_PER_BIT_BASE_IT;
+ lux = div_u64(lux, als_it);

ret = i2c_smbus_read_word_data(client, CM32181_REG_ADDR_ALS);
if (ret < 0)
@@ -220,8 +220,8 @@ static int cm32181_get_lux(struct cm32181_chip *cm32181)

lux *= ret;
lux *= cm32181->calibscale;
- lux /= CM32181_CALIBSCALE_RESOLUTION;
- lux /= MLUX_PER_LUX;
+ lux = div_u64(lux, CM32181_CALIBSCALE_RESOLUTION);
+ lux = div_u64(lux, CM32181_LUX_PER_BIT_RESOLUTION);

if (lux > 0xFFFF)
lux = 0xFFFF;
--
2.26.0