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    SubjectRe: [PATCH v2] iio: afe: rescale: Accept only offset channels
    On Sat, 02 Sep 2023 21:46:20 +0200
    Linus Walleij <linus.walleij@linaro.org> wrote:

    > 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>

    Peter, can you take a look at this v2?

    Thanks,

    Jonathan
    > ---
    > Changes in v2:
    > - Fix rescale_read_raw() handle channels with offset but no scale.
    > - Link to v1: https://lore.kernel.org/r/20230830-iio-rescale-only-offset-v1-1-40ab9f4436c7@linaro.org
    > ---
    > drivers/iio/afe/iio-rescale.c | 19 +++++++++++++++----
    > 1 file changed, 15 insertions(+), 4 deletions(-)
    >
    > diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
    > index 1f280c360701..56e5913ab82d 100644
    > --- 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;
    >
    > ---
    > base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
    > change-id: 20230830-iio-rescale-only-offset-f28e05bd2deb
    >
    > Best regards,

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