[PATCH v2 4/5] max44000: Expose ambient sensor scaling

From: Crestez Dan Leonard
Date: Mon Apr 11 2016 - 14:53:14 EST

This patch exposes ALSTIM as illuminance_integration_time and ALSPGA as
illuminance_scale.

Changing ALSTIM also changes the number of bits available in the data
register. This is handled inside raw value reading because:
* It's very easy to shift a few bits
* It allows SCALE and INT_TIME to be completely independent controls
* Buffer support requires constant scan_type.realbits per-channel

Signed-off-by: Crestez Dan Leonard <leonard.crestez@xxxxxxxxx>
---
drivers/iio/light/max44000.c | 164 +++++++++++++++++++++++++++++++++++++++++--
1 file changed, 160 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/light/max44000.c b/drivers/iio/light/max44000.c
index 662a45b..79a8282 100644
--- a/drivers/iio/light/max44000.c
+++ b/drivers/iio/light/max44000.c
@@ -59,6 +59,12 @@
*/
#define MAX44000_REG_CFG_RX_DEFAULT 0xf0

+/* REG_RX bits */
+#define MAX44000_CFG_RX_ALSTIM_MASK 0x0c
+#define MAX44000_CFG_RX_ALSTIM_SHIFT 2
+#define MAX44000_CFG_RX_ALSPGA_MASK 0x03
+#define MAX44000_CFG_RX_ALSPGA_SHIFT 0
+
/* REG_TX bits */
#define MAX44000_LED_CURRENT_MASK 0xf
#define MAX44000_LED_CURRENT_MAX 11
@@ -112,6 +118,51 @@ struct max44000_data {
/* Default scale is set to the minimum of 0.03125 or 1 / (1 << 5) lux */
#define MAX44000_ALS_TO_LUX_DEFAULT_FRACTION_LOG2 5

+/* Scale can be multiplied by up to 128x via ALSPGA for measurement gain */
+static const int max44000_alspga_shift[] = {0, 2, 4, 7};
+#define MAX44000_ALSPGA_MAX_SHIFT 7
+
+/*
+ * Scale can be multiplied by up to 64x via ALSTIM because of lost resolution
+ *
+ * This scaling factor is hidden from userspace and instead accounted for when
+ * reading raw values from the device.
+ *
+ * This makes it possible to cleanly expose ALSPGA as IIO_CHAN_INFO_SCALE and
+ * ALSTIM as IIO_CHAN_INFO_INT_TIME without the values affecting each other.
+ *
+ * Handling this internally is also required for buffer support because the
+ * channel's scan_type can't be modified dynamically.
+ */
+static const int max44000_alstim_shift[] = {0, 2, 4, 6};
+#define MAX44000_ALSTIM_SHIFT(alstim) (2 * (alstim))
+
+/* Available integration times with pretty manual alignment: */
+static const int max44000_int_time_avail_ns_array[] = {
+ 100000000,
+ 25000000,
+ 6250000,
+ 1562500,
+};
+static const char max44000_int_time_avail_str[] =
+ "0.100 "
+ "0.025 "
+ "0.00625 "
+ "0.001625";
+
+/* Available scales (internal to ulux) with pretty manual alignment: */
+static const int max44000_scale_avail_ulux_array[] = {
+ 31250,
+ 125000,
+ 500000,
+ 4000000,
+};
+static const char max44000_scale_avail_str[] =
+ "0.03125 "
+ "0.125 "
+ "0.5 "
+ "4";
+
static const struct iio_chan_spec max44000_channels[] = {
{
.type = IIO_LIGHT,
@@ -133,15 +184,54 @@ static const struct iio_chan_spec max44000_channels[] = {
},
};

+static int max44000_read_alstim(struct max44000_data *data)
+{
+ unsigned int val;
+ int ret;
+
+ ret = regmap_read(data->regmap, MAX44000_REG_CFG_RX, &val);
+ if (ret < 0)
+ return ret;
+ return (val & MAX44000_CFG_RX_ALSTIM_MASK) >> MAX44000_CFG_RX_ALSTIM_SHIFT;
+}
+
+static int max44000_write_alstim(struct max44000_data *data, int val)
+{
+ return regmap_write_bits(data->regmap, MAX44000_REG_CFG_RX,
+ MAX44000_CFG_RX_ALSTIM_MASK,
+ val << MAX44000_CFG_RX_ALSTIM_SHIFT);
+}
+
+static int max44000_read_alspga(struct max44000_data *data)
+{
+ unsigned int val;
+ int ret;
+
+ ret = regmap_read(data->regmap, MAX44000_REG_CFG_RX, &val);
+ if (ret < 0)
+ return ret;
+ return (val & MAX44000_CFG_RX_ALSPGA_MASK) >> MAX44000_CFG_RX_ALSPGA_SHIFT;
+}
+
+static int max44000_write_alspga(struct max44000_data *data, int val)
+{
+ return regmap_write_bits(data->regmap, MAX44000_REG_CFG_RX,
+ MAX44000_CFG_RX_ALSPGA_MASK,
+ val << MAX44000_CFG_RX_ALSPGA_SHIFT);
+}
+
static int max44000_read_alsval(struct max44000_data *data)
{
u16 regval;
- int ret;
+ int alstim, ret;

ret = regmap_bulk_read(data->regmap, MAX44000_REG_ALS_DATA_HI,
&regval, sizeof(regval));
if (ret < 0)
return ret;
+ alstim = ret = max44000_read_alstim(data);
+ if (ret < 0)
+ return ret;

regval = be16_to_cpu(regval);

@@ -157,7 +247,7 @@ static int max44000_read_alsval(struct max44000_data *data)
if (regval & MAX44000_ALSDATA_OVERFLOW)
return 0x3FFF;

- return regval;
+ return regval << MAX44000_ALSTIM_SHIFT(alstim);
}

static int max44000_write_led_current_raw(struct max44000_data *data, int val)
@@ -190,6 +280,7 @@ static int max44000_read_raw(struct iio_dev *indio_dev,
int *val, int *val2, long mask)
{
struct max44000_data *data = iio_priv(indio_dev);
+ int alstim, alspga;
unsigned int regval;
int ret;

@@ -235,14 +326,34 @@ static int max44000_read_raw(struct iio_dev *indio_dev,
return IIO_VAL_INT;

case IIO_LIGHT:
- *val = 1;
- *val2 = MAX44000_ALS_TO_LUX_DEFAULT_FRACTION_LOG2;
+ mutex_lock(&data->lock);
+ alspga = ret = max44000_read_alspga(data);
+ mutex_unlock(&data->lock);
+ if (ret < 0)
+ return ret;
+
+ /* Avoid negative shifts */
+ *val = (1 << MAX44000_ALSPGA_MAX_SHIFT);
+ *val2 = MAX44000_ALS_TO_LUX_DEFAULT_FRACTION_LOG2
+ + MAX44000_ALSPGA_MAX_SHIFT
+ - max44000_alspga_shift[alspga];
return IIO_VAL_FRACTIONAL_LOG2;

default:
return -EINVAL;
}

+ case IIO_CHAN_INFO_INT_TIME:
+ mutex_lock(&data->lock);
+ alstim = ret = max44000_read_alstim(data);
+ mutex_unlock(&data->lock);
+
+ if (ret < 0)
+ return ret;
+ *val = 0;
+ *val2 = max44000_int_time_avail_ns_array[alstim];
+ return IIO_VAL_INT_PLUS_NANO;
+
default:
return -EINVAL;
}
@@ -260,15 +371,60 @@ static int max44000_write_raw(struct iio_dev *indio_dev,
ret = max44000_write_led_current_raw(data, val);
mutex_unlock(&data->lock);
return ret;
+ } else if (mask == IIO_CHAN_INFO_INT_TIME && chan->type == IIO_LIGHT) {
+ s64 valns = val * NSEC_PER_SEC + val2;
+ int alstim = find_closest_descending(valns,
+ max44000_int_time_avail_ns_array,
+ ARRAY_SIZE(max44000_int_time_avail_ns_array));
+ mutex_lock(&data->lock);
+ ret = max44000_write_alstim(data, alstim);
+ mutex_unlock(&data->lock);
+ return ret;
+ } else if (mask == IIO_CHAN_INFO_SCALE && chan->type == IIO_LIGHT) {
+ s64 valus = val * USEC_PER_SEC + val2;
+ int alspga = find_closest(valus,
+ max44000_scale_avail_ulux_array,
+ ARRAY_SIZE(max44000_scale_avail_ulux_array));
+ mutex_lock(&data->lock);
+ ret = max44000_write_alspga(data, alspga);
+ mutex_unlock(&data->lock);
+ return ret;
}

return -EINVAL;
}

+static int max44000_write_raw_get_fmt(struct iio_dev *indio_dev,
+ struct iio_chan_spec const *chan,
+ long mask)
+{
+ if (mask == IIO_CHAN_INFO_INT_TIME && chan->type == IIO_LIGHT)
+ return IIO_VAL_INT_PLUS_NANO;
+ else if (mask == IIO_CHAN_INFO_SCALE && chan->type == IIO_LIGHT)
+ return IIO_VAL_INT_PLUS_MICRO;
+ else
+ return IIO_VAL_INT;
+}
+
+static IIO_CONST_ATTR(illuminance_integration_time_available, max44000_int_time_avail_str);
+static IIO_CONST_ATTR(illuminance_scale_available, max44000_scale_avail_str);
+
+static struct attribute *max44000_attributes[] = {
+ &iio_const_attr_illuminance_integration_time_available.dev_attr.attr,
+ &iio_const_attr_illuminance_scale_available.dev_attr.attr,
+ NULL
+};
+
+static const struct attribute_group max44000_attribute_group = {
+ .attrs = max44000_attributes,
+};
+
static const struct iio_info max44000_info = {
.driver_module = THIS_MODULE,
.read_raw = max44000_read_raw,
.write_raw = max44000_write_raw,
+ .write_raw_get_fmt = max44000_write_raw_get_fmt,
+ .attrs = &max44000_attribute_group,
};

static bool max44000_readable_reg(struct device *dev, unsigned int reg)
--
2.5.5