[PATCH v2] iio: afe: iio-rescale: Support processed channels

[Linus Walleij <linus.walleij@linaro.org>]

It happens that an ADC will only provide raw or processed
voltage conversion channels. (adc/ab8500-gpadc.c).
On the Samsung GT-I9070 this is used for a light sensor
and current sense amplifier so we need to think of something.

The idea is to allow processed channels and scale them
with 1/1 and then the rescaler can modify the result
on top.

Link: https://lore.kernel.org/linux-iio/20201101232211.1194304-1-linus.walleij@linaro.org/
Cc: Peter Rosin <peda@axentia.se>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
ChangeLog v1->v2:
- Deny calls to .read_avail() for processed channels, and
  insert a comment.
- Move an assignment of IIO_VAL_FRACTIONAL down to the end
  of the block for better readability.
---
 drivers/iio/afe/iio-rescale.c | 39 +++++++++++++++++++++++++++++++----
 1 file changed, 35 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index e42ea2b1707d..ddbb760ae8df 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -29,6 +29,7 @@ struct rescale {
 	struct iio_channel *source;
 	struct iio_chan_spec chan;
 	struct iio_chan_spec_ext_info *ext_info;
+	bool chan_processed;
 	s32 numerator;
 	s32 denominator;
 };
@@ -43,10 +44,27 @@ static int rescale_read_raw(struct iio_dev *indio_dev,
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
-		return iio_read_channel_raw(rescale->source, val);
+		if (rescale->chan_processed)
+			/*
+			 * When only processed channels are supported, we
+			 * read the processed data and scale it by 1/1
+			 * augmented with whatever the rescaler has calculated.
+			 */
+			return iio_read_channel_processed(rescale->source, val);
+		else
+			return iio_read_channel_raw(rescale->source, val);
 
 	case IIO_CHAN_INFO_SCALE:
-		ret = iio_read_channel_scale(rescale->source, val, val2);
+		if (rescale->chan_processed) {
+			/*
+			 * Processed channels are scaled 1-to-1
+			 */
+			*val = 1;
+			*val2 = 1;
+			ret = IIO_VAL_FRACTIONAL;
+		} else {
+			ret = iio_read_channel_scale(rescale->source, val, val2);
+		}
 		switch (ret) {
 		case IIO_VAL_FRACTIONAL:
 			*val *= rescale->numerator;
@@ -82,6 +100,14 @@ static int rescale_read_avail(struct iio_dev *indio_dev,
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
+		/*
+		 * Using .read_avail() is fringe to begin with and makes
+		 * no sense whatsoever for processed channels, so if called
+		 * on a processed channel, we just error out here.
+		 */
+		if (rescale->chan_processed)
+			return -EINVAL;
+
 		*type = IIO_VAL_INT;
 		return iio_read_avail_channel_raw(rescale->source,
 						  vals, length);
@@ -132,8 +158,13 @@ static int rescale_configure_channel(struct device *dev,
 
 	if (!iio_channel_has_info(schan, IIO_CHAN_INFO_RAW) ||
 	    !iio_channel_has_info(schan, IIO_CHAN_INFO_SCALE)) {
-		dev_err(dev, "source channel does not support raw/scale\n");
-		return -EINVAL;
+		if (iio_channel_has_info(schan, IIO_CHAN_INFO_PROCESSED)) {
+			dev_info(dev, "using processed channel\n");
+			rescale->chan_processed = true;
+		} else {
+			dev_err(dev, "source channel does not support raw+scale or processed data\n");
+			return -EINVAL;
+		}
 	}
 
 	chan->info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
-- 
2.30.2