On Sun, Mar 07, 2021 at 12:20:04AM +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() 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. > > Since the old iio_read_channel_processed() would > lose precision if we fall back to reading raw and > scaling, we introduce a new API that will pass in > the scale factor, iio_read_channel_processed_scale(), > as part of this patch. > > 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@xxxxxxxxx> > 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> > --- > 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 ++++++++++++++++++--------- > drivers/iio/inkern.c | 15 +++++++++++++-- > include/linux/iio/consumer.h | 15 +++++++++++++++ No matter which branch this is merged through, it should be several patches, one to introduce the API and one to start using it. Guenter > 3 files changed, 46 insertions(+), 11 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; > diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c > index db77a2d4a56b..6a842c6b6705 100644 > --- a/drivers/iio/inkern.c > +++ b/drivers/iio/inkern.c > @@ -688,7 +688,8 @@ int iio_read_channel_offset(struct iio_channel *chan, int *val, int *val2) > } > EXPORT_SYMBOL_GPL(iio_read_channel_offset); > > -int iio_read_channel_processed(struct iio_channel *chan, int *val) > +int iio_read_channel_processed_scale(struct iio_channel *chan, int *val, > + unsigned int scale) > { > int ret; > > @@ -701,11 +702,14 @@ int iio_read_channel_processed(struct iio_channel *chan, int *val) > if (iio_channel_has_info(chan->channel, IIO_CHAN_INFO_PROCESSED)) { > ret = iio_channel_read(chan, val, NULL, > IIO_CHAN_INFO_PROCESSED); > + if (!ret) > + *val *= scale; > } else { > ret = iio_channel_read(chan, val, NULL, IIO_CHAN_INFO_RAW); > if (ret < 0) > goto err_unlock; > - ret = iio_convert_raw_to_processed_unlocked(chan, *val, val, 1); > + ret = iio_convert_raw_to_processed_unlocked(chan, *val, val, > + scale); > } > > err_unlock: > @@ -713,6 +717,13 @@ int iio_read_channel_processed(struct iio_channel *chan, int *val) > > return ret; > } > +EXPORT_SYMBOL_GPL(iio_read_channel_processed_scale); > + > +int iio_read_channel_processed(struct iio_channel *chan, int *val) > +{ > + /* This is just a special case with scale factor 1 */ > + return iio_read_channel_processed_scale(chan, val, 1); > +} > EXPORT_SYMBOL_GPL(iio_read_channel_processed); > > int iio_read_channel_scale(struct iio_channel *chan, int *val, int *val2) > diff --git a/include/linux/iio/consumer.h b/include/linux/iio/consumer.h > index 0a90ba8fa1bb..5fa5957586cf 100644 > --- a/include/linux/iio/consumer.h > +++ b/include/linux/iio/consumer.h > @@ -241,6 +241,21 @@ int iio_read_channel_average_raw(struct iio_channel *chan, int *val); > */ > int iio_read_channel_processed(struct iio_channel *chan, int *val); > > +/** > + * iio_read_channel_processed_scale() - read and scale a processed value > + * @chan: The channel being queried. > + * @val: Value read back. > + * @scale: Scale factor to apply during the conversion > + * > + * Returns an error code or 0. > + * > + * This function will read a processed value from a channel. This will work > + * like @iio_read_channel_processed() but also scale with an additional > + * scale factor while attempting to minimize any precision loss. > + */ > +int iio_read_channel_processed_scale(struct iio_channel *chan, int *val, > + unsigned int scale); > + > /** > * iio_write_channel_attribute() - Write values to the device attribute. > * @chan: The channel being queried. > -- > 2.29.2 >
