iio: afe: rescale: Accept only offset channels

As noted by Jonathan Cameron: it is perfectly legal for a channel
to have an offset but no scale in addition to the raw interface.
The conversion will imply that scale is 1:1.

Make rescale_configure_channel() accept just scale, or just offset
to process a channel.

When a user asks for IIO_CHAN_INFO_OFFSET in rescale_read_raw()
we now have to deal with the fact that OFFSET could be present
but SCALE missing. Add code to simply scale 1:1 in this case.

Link: https://lore.kernel.org/linux-iio/CACRpkdZXBjHU4t-GVOCFxRO-AHGxKnxMeHD2s4Y4PuC29gBq6g@mail.gmail.com/
Fixes: 53ebee949980 ("iio: afe: iio-rescale: Support processed channels")
Fixes: 9decacd8b3a4 ("iio: afe: rescale: Fix boolean logic bug")
Reported-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Peter Rosin <peda@axentia.se>
Link: https://lore.kernel.org/r/20230902-iio-rescale-only-offset-v2-1-988b807754c8@linaro.org
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index 1f280c360701bc333fad01c4c07d3e34a914ea32..56e5913ab82d1c045c9ca27012008a4495502cbf 100644 (file)
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -214,8 +214,18 @@ static int rescale_read_raw(struct iio_dev *indio_dev,
                                return ret < 0 ? ret : -EOPNOTSUPP;
                }
 
-               ret = iio_read_channel_scale(rescale->source, &scale, &scale2);
-               return rescale_process_offset(rescale, ret, scale, scale2,
+               if (iio_channel_has_info(rescale->source->channel,
+                                        IIO_CHAN_INFO_SCALE)) {
+                       ret = iio_read_channel_scale(rescale->source, &scale, &scale2);
+                       return rescale_process_offset(rescale, ret, scale, scale2,
+                                                     schan_off, val, val2);
+               }
+
+               /*
+                * If we get here we have no scale so scale 1:1 but apply
+                * rescaler and offset, if any.
+                */
+               return rescale_process_offset(rescale, IIO_VAL_FRACTIONAL, 1, 1,
                                              schan_off, val, val2);
        default:
                return -EINVAL;
@@ -280,8 +290,9 @@ static int rescale_configure_channel(struct device *dev,
        chan->type = rescale->cfg->type;
 
        if (iio_channel_has_info(schan, IIO_CHAN_INFO_RAW) &&
-           iio_channel_has_info(schan, IIO_CHAN_INFO_SCALE)) {
-               dev_info(dev, "using raw+scale source channel\n");
+           (iio_channel_has_info(schan, IIO_CHAN_INFO_SCALE) ||
+            iio_channel_has_info(schan, IIO_CHAN_INFO_OFFSET))) {
+               dev_info(dev, "using raw+scale/offset source channel\n");
        } else if (iio_channel_has_info(schan, IIO_CHAN_INFO_PROCESSED)) {
                dev_info(dev, "using processed channel\n");
                rescale->chan_processed = true;