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iio: adc: ti-ads1015: add adequate wait time to get correct conversion 

This driver assumes that the device is operating in the continuous
conversion mode which performs the conversion continuously.  So this driver
inserts a wait time before reading the conversion register if the
configuration is changed from a previous request.

Currently, the wait time is only the period required for a single
conversion that is calculated as the reciprocal of the sampling frequency.
However we also need to wait for the the previous conversion to complete.
Otherwise we probably get the conversion result for the previous
configuration when the sampling frequency is lower.

Cc: Daniel Baluta <daniel.baluta@gmail.com>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
This commit is contained in:
Akinobu Mita 2017-07-21 00:24:22 +09:00 committed by Jonathan Cameron
parent a6fe5e52d5
commit 4744d4e2af
1 changed files with 22 additions and 15 deletions
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37
drivers/iio/adc/ti-ads1015.c
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@ -242,27 +242,34 @@ static
int ads1015_get_adc_result(struct ads1015_data *data, int chan, int *val)
{
int ret, pga, dr, conv_time;
bool change;
unsigned int old, mask, cfg;
if (chan < 0 || chan >= ADS1015_CHANNELS)
return -EINVAL;
pga = data->channel_data[chan].pga;
dr = data->channel_data[chan].data_rate;
ret = regmap_update_bits_check(data->regmap, ADS1015_CFG_REG,
ADS1015_CFG_MUX_MASK |
ADS1015_CFG_PGA_MASK |
ADS1015_CFG_DR_MASK,
chan << ADS1015_CFG_MUX_SHIFT |
pga << ADS1015_CFG_PGA_SHIFT |
dr << ADS1015_CFG_DR_SHIFT,
&change);
if (ret < 0)
ret = regmap_read(data->regmap, ADS1015_CFG_REG, &old);
if (ret)
return ret;
if (change || data->conv_invalid) {
conv_time = DIV_ROUND_UP(USEC_PER_SEC, data->data_rate[dr]);
pga = data->channel_data[chan].pga;
dr = data->channel_data[chan].data_rate;
mask = ADS1015_CFG_MUX_MASK | ADS1015_CFG_PGA_MASK |
ADS1015_CFG_DR_MASK;
cfg = chan << ADS1015_CFG_MUX_SHIFT | pga << ADS1015_CFG_PGA_SHIFT |
dr << ADS1015_CFG_DR_SHIFT;
cfg = (old & ~mask) | (cfg & mask);
ret = regmap_write(data->regmap, ADS1015_CFG_REG, cfg);
if (ret)
return ret;
if (old != cfg || data->conv_invalid) {
int dr_old = (old & ADS1015_CFG_DR_MASK) >>
ADS1015_CFG_DR_SHIFT;
conv_time = DIV_ROUND_UP(USEC_PER_SEC, data->data_rate[dr_old]);
conv_time += DIV_ROUND_UP(USEC_PER_SEC, data->data_rate[dr]);
usleep_range(conv_time, conv_time + 1);
data->conv_invalid = false;
}