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    SubjectRe: [PATCH] iio: afe: rescale: Accept only offset channels
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    Hi!

    2023-08-30 at 10:52, Linus Walleij 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.
    >
    > The code to handle channels with just offset is already there.
    >
    > 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>
    > ---
    > drivers/iio/afe/iio-rescale.c | 5 +++--
    > 1 file changed, 3 insertions(+), 2 deletions(-)
    >
    > diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
    > index 1f280c360701..18aafb4bdda0 100644
    > --- a/drivers/iio/afe/iio-rescale.c
    > +++ b/drivers/iio/afe/iio-rescale.c
    > @@ -280,8 +280,9 @@ 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");

    I do not think it's that simple. The rescale_read_raw function, when asked
    for IIO_CHAN_INFO_OFFSET, must know the scale of the source channel in
    order to rescale the offset. After this patch, trying to get the rescaled
    scale/offset when the source channel has an offset but lacks a scale will
    simply return -EOPNOTSUPP.

    Which is not what you intended, I think?

    Cheers,
    Peter

    > } 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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