On 06/01/2015 09:27 AM, Chris Lesiak wrote:
The function ntc_adc_iio_read was assuming both a 12 bit ADC and that
pullup_uv is the same as the ADC reference voltage. If either
assumption is false, then the result is incorrect.
Attempt to use iio_convert_raw_to_processed to convert the raw value to
microvolts. It will fail for iio channels that don't support support
But we need millivolts ?
Guenter
IIO_CHAN_INFO_SCALE; in that case fall back to the assumptions.
Signed-off-by: Chris Lesiak <chris.lesiak@xxxxxxxxx>
---
drivers/hwmon/ntc_thermistor.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)
This patch was previously titled:
"hwmon: ntc: use iio_read_channel_processed if possible"
but that doesn't describe it anymore.
Changes in v3
=============
- Don't use iio_read_channel_processed because it does not return results in
microvolts.
- Do use iio_convert_raw_to_processed with a scale factor of 1000 to get
microvolts instead of the iio normal unit of millivolts.
- Do it all in the context of the original ntc_adc_iio_read function instead
of having separate read functions for the raw and processed cases.
diff --git a/drivers/hwmon/ntc_thermistor.c b/drivers/hwmon/ntc_thermistor.c
index 6880011..e08ed47 100644
--- a/drivers/hwmon/ntc_thermistor.c
+++ b/drivers/hwmon/ntc_thermistor.c
@@ -190,20 +190,21 @@ struct ntc_data {
static int ntc_adc_iio_read(struct ntc_thermistor_platform_data *pdata)
{
struct iio_channel *channel = pdata->chan;
- s64 result;
- int val, ret;
+ int raw, uv, ret;
- ret = iio_read_channel_raw(channel, &val);
+ ret = iio_read_channel_raw(channel, &raw);
if (ret < 0) {
pr_err("read channel() error: %d\n", ret);
return ret;
}
- /* unit: mV */
- result = pdata->pullup_uv * (s64) val;
- result >>= 12;
+ ret = iio_convert_raw_to_processed(channel, raw, &uv, 1000);
+ if (ret < 0) {
+ /* Assume 12 bit ADC with vref at pullup_uv*/
+ uv = (pdata->pullup_uv * (s64)raw) >> 12;
+ }
- return (int)result;
+ return uv;
}
static const struct of_device_id ntc_match[] = {
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