[PATCH v11 06/15] iio: afe: rescale: add offset support

Liam Beguin
2021-12-22T03:47:09Z

From: Liam Beguin <lvb@xiphos.com>

This is a preparatory change required for the addition of temperature
sensing front ends.

Signed-off-by: Liam Beguin <lvb@xiphos.com>
---
drivers/iio/afe/iio-rescale.c | 80 +++++++++++++++++++++++++++++++++
include/linux/iio/afe/rescale.h | 4 ++
2 files changed, 84 insertions(+)

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index 190a83e08008..6a2d4ae80652 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -81,11 +81,46 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
}
}

+int rescale_process_offset(struct rescale *rescale, int scale_type,
+ int scale, int scale2, int schan_off,
+ int *val, int *val2)
+{
+ s64 tmp, tmp2;
+
+ switch (scale_type) {
+ case IIO_VAL_FRACTIONAL:
+ tmp = (s64)rescale->offset * scale2;
+ *val = div_s64(tmp, scale) + schan_off;
+ return IIO_VAL_INT;
+ case IIO_VAL_INT:
+ *val = div_s64(rescale->offset, scale) + schan_off;
+ return IIO_VAL_INT;
+ case IIO_VAL_FRACTIONAL_LOG2:
+ tmp = (s64)rescale->offset * (1 << scale2);
+ *val = div_s64(tmp, scale) + schan_off;
+ return IIO_VAL_INT;
+ case IIO_VAL_INT_PLUS_NANO:
+ tmp = (s64)rescale->offset * NANO;
+ tmp2 = ((s64)scale * NANO) + scale2;
+ *val = div64_s64(tmp, tmp2) + schan_off;
+ return IIO_VAL_INT;
+ case IIO_VAL_INT_PLUS_MICRO:
+ tmp = (s64)rescale->offset * MICRO;
+ tmp2 = ((s64)scale * MICRO) + scale2;
+ *val = div64_s64(tmp, tmp2) + schan_off;
+ return IIO_VAL_INT;
+ default:
+ return -EOPNOTSUPP;
+ }
+}
+
static int rescale_read_raw(struct iio_dev *indio_dev,
struct iio_chan_spec const *chan,
int *val, int *val2, long mask)
{
struct rescale *rescale = iio_priv(indio_dev);
+ int scale, scale2;
+ int schan_off = 0;
int ret;

switch (mask) {
@@ -112,6 +147,47 @@ static int rescale_read_raw(struct iio_dev *indio_dev,
ret = iio_read_channel_scale(rescale->source, val, val2);
}
return rescale_process_scale(rescale, ret, val, val2);
+ case IIO_CHAN_INFO_OFFSET:
+ /*
+ * Processed channels are scaled 1-to-1 and source offset is
+ * already taken into account.
+ *
+ * In other cases, real world measurement are expressed as:
+ *
+ * schan_scale * (raw + schan_offset)
+ *
+ * Given that the rescaler parameters are applied recursively:
+ *
+ * rescaler_scale * (schan_scale * (raw + schan_offset) +
+ * rescaler_offset)
+ *
+ * Or,
+ *
+ * (rescaler_scale * schan_scale) * (raw +
+ * (schan_offset + rescaler_offset / schan_scale)
+ *
+ * Thus, reusing the original expression the parameters exposed
+ * to userspace are:
+ *
+ * scale = schan_scale * rescaler_scale
+ * offset = schan_offset + rescaler_offset / schan_scale
+ */
+ if (rescale->chan_processed) {
+ *val = rescale->offset;
+ return IIO_VAL_INT;
+ }
+
+ if (iio_channel_has_info(rescale->source->channel,
+ IIO_CHAN_INFO_OFFSET)) {
+ ret = iio_read_channel_offset(rescale->source,
+ &schan_off, NULL);
+ if (ret != IIO_VAL_INT)
+ return ret < 0 ? ret : -EOPNOTSUPP;
+ }
+
+ ret = iio_read_channel_scale(rescale->source, &scale, &scale2);
+ return rescale_process_offset(rescale, ret, scale, scale2,
+ schan_off, val, val2);
default:
return -EINVAL;
}
@@ -188,6 +264,9 @@ static int rescale_configure_channel(struct device *dev,
chan->info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
BIT(IIO_CHAN_INFO_SCALE);

+ if (rescale->offset)
+ chan->info_mask_separate |= BIT(IIO_CHAN_INFO_OFFSET);
+
/*
* Using .read_avail() is fringe to begin with and makes no sense
* whatsoever for processed channels, so we make sure that this cannot
@@ -352,6 +431,7 @@ static int rescale_probe(struct platform_device *pdev)
rescale->cfg = of_device_get_match_data(dev);
rescale->numerator = 1;
rescale->denominator = 1;
+ rescale->offset = 0;

ret = rescale->cfg->props(dev, rescale);
if (ret)
diff --git a/include/linux/iio/afe/rescale.h b/include/linux/iio/afe/rescale.h
index 14d4ee1227c6..b152ac487403 100644
--- a/include/linux/iio/afe/rescale.h
+++ b/include/linux/iio/afe/rescale.h
@@ -23,8 +23,12 @@ struct rescale {
bool chan_processed;
s32 numerator;
s32 denominator;
+ s32 offset;
};

int rescale_process_scale(struct rescale *rescale, int scale_type,
int *val, int *val2);
+int rescale_process_offset(struct rescale *rescale, int scale_type,
+ int scale, int scale2, int schan_off,
+ int *val, int *val2);
#endif /* __IIO_RESCALE_H__ */
--
2.34.0