From 431e9147b4667d67399fe5db4f8203d55811951b Mon Sep 17 00:00:00 2001 From: Jonathan Cameron Date: Sun, 26 Jun 2022 13:29:31 +0100 Subject: [PATCH] staging: iio: cdc: ad7746: Use _raw and _scale for temperature channels. Performing the maths to rescale a 24 bit raw reading within the driver was resulting in precision losses. So make that userspace's problem by exporting the scale and letting the maths be done in userspace with appropriate precision. Issue identified using roadtester testing framework. Signed-off-by: Jonathan Cameron Reviewed-by: Andy Shevchenko Link: https://lore.kernel.org/r/20220626122938.582107-11-jic23@kernel.org --- drivers/staging/iio/cdc/ad7746.c | 23 ++++++++--------------- 1 file changed, 8 insertions(+), 15 deletions(-) diff --git a/drivers/staging/iio/cdc/ad7746.c b/drivers/staging/iio/cdc/ad7746.c index 81be645f08c5b..3e8e7836a5831 100644 --- a/drivers/staging/iio/cdc/ad7746.c +++ b/drivers/staging/iio/cdc/ad7746.c @@ -178,14 +178,16 @@ static const struct iio_chan_spec ad7746_channels[] = { .type = IIO_TEMP, .indexed = 1, .channel = 0, - .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), + .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), + .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE), .address = TEMP_INT, }, [TEMP_EXT] = { .type = IIO_TEMP, .indexed = 1, .channel = 1, - .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED), + .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), + .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE), .address = TEMP_EXT, }, [CIN1] = { @@ -581,18 +583,6 @@ static int ad7746_read_channel(struct iio_dev *indio_dev, *val = get_unaligned_be24(data) - 0x800000; - switch (chan->type) { - case IIO_TEMP: - /* - * temperature in milli degrees Celsius - * T = ((*val / 2048) - 4096) * 1000 - */ - *val = (*val * 125) / 256; - break; - default: - break; - } - return 0; } @@ -607,7 +597,6 @@ static int ad7746_read_raw(struct iio_dev *indio_dev, switch (mask) { case IIO_CHAN_INFO_RAW: - case IIO_CHAN_INFO_PROCESSED: mutex_lock(&chip->lock); ret = ad7746_read_channel(indio_dev, chan, val); mutex_unlock(&chip->lock); @@ -666,6 +655,10 @@ static int ad7746_read_raw(struct iio_dev *indio_dev, *val *= 6; *val2 = 23; return IIO_VAL_FRACTIONAL_LOG2; + case IIO_TEMP: + *val = 125; + *val2 = 8; + return IIO_VAL_FRACTIONAL_LOG2; default: return -EINVAL; } -- 2.30.2