On Mon, Mar 08, 2021 at 11:02:19AM +0100, Linus Walleij wrote: > Before trying the custom method of reading the sensor > as raw and then converting, we want to use > iio_read_channel_processed_scale() which first tries to > see if the ADC can provide a processed value directly, > else reads raw and applies scaling inside of IIO > using the scale attributes of the ADC. We need to > multiply the scaled value with 1000 to get to > microvolts from millivolts which is what processed > IIO channels returns. > > Keep the code that assumes 12bit ADC around as a > fallback. > > This gives correct readings on the AB8500 thermistor > inputs used in the Ux500 HREFP520 platform for reading > battery and board temperature. > > Cc: Peter Rosin <peda@xxxxxxxxxx> > Cc: Chris Lesiak <chris.lesiak@xxxxxxxxx> > Cc: Jonathan Cameron <jic23@xxxxxxxxxx> > Cc: linux-iio@xxxxxxxxxxxxxxx > Link: https://lore.kernel.org/linux-iio/20201224011607.1059534-1-linus.walleij@xxxxxxxxxx/ > Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx> Acked-by: Guenter Roeck <linux@xxxxxxxxxxxx> Up to Jonathan to decide if he wants to take both patches. Thanks, Guenter > --- > ChangeLog v3->v4: > - Split out the new iio_read_channel_processed_scale() > API addition to a separate patch. > - My suggestion is to apply both patches to the hwmon > tree. > ChangeLog v2->v3: > - After discussion about v2 we concludes that > iio_read_channel_processed() could loose precision > so we introduce a new API to read processed and > scale. > - Include a link to the v2 discussion for reference. > - For ease of applying to the hwmon tree, keep it all > in one patch. > - This needs Jonathans ACK to be merged through hwmon. > ChangeLog v1->v2: > - Fix the patch to multiply the processed value by > 1000 to get to microvolts from millivolts. > - Fix up the confusion in the commit message. > - Drop pointless comments about the code, we keep the > original code path around if processed reads don't > work, nothing bad with that. > --- > drivers/hwmon/ntc_thermistor.c | 27 ++++++++++++++++++--------- > 1 file changed, 18 insertions(+), 9 deletions(-) > > diff --git a/drivers/hwmon/ntc_thermistor.c b/drivers/hwmon/ntc_thermistor.c > index 3aad62a0e661..8587189c7f15 100644 > --- a/drivers/hwmon/ntc_thermistor.c > +++ b/drivers/hwmon/ntc_thermistor.c > @@ -326,18 +326,27 @@ struct ntc_data { > static int ntc_adc_iio_read(struct ntc_thermistor_platform_data *pdata) > { > struct iio_channel *channel = pdata->chan; > - int raw, uv, ret; > + int uv, ret; > > - ret = iio_read_channel_raw(channel, &raw); > + ret = iio_read_channel_processed_scale(channel, &uv, 1000); > if (ret < 0) { > - pr_err("read channel() error: %d\n", ret); > - return ret; > - } > + int raw; > > - 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; > + /* > + * This fallback uses a raw read and then > + * assumes the ADC is 12 bits, scaling with > + * a factor 1000 to get to microvolts. > + */ > + ret = iio_read_channel_raw(channel, &raw); > + if (ret < 0) { > + pr_err("read channel() error: %d\n", ret); > + return ret; > + } > + 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 uv; > -- > 2.29.2 >
