Re: [PATCH] drivers: iio: adc: ltc2497: fix LSB shift

Jonathan Cameron
2023-01-27T17:48:05Z

On Fri, 27 Jan 2023 14:57:14 +0200
Ian Ray <ian.ray@ge.com> wrote:

> Correct the "sub_lsb" shift for both ltc2497 and ltc2499.

Hi Iain, Thanks for the patch.

>
> An earlier version of the code shifted by 14 but this was a consequence
> of reading three bytes into a __be32 buffer and using be32_to_cpu(), so
> eight extra bits needed to be skipped. Now we use get_unaligned_be24()
> and thus the additional skip is wrong.
>
> Fixes 2187cfe ("drivers: iio: adc: ltc2497: LTC2499 support")

This isn't in standard Fixes tag format. If nothing else comes
up I'll fix up whilst applying.

> Signed-off-by: Ian Ray <ian.ray@ge.com>
> ---
> drivers/iio/adc/ltc2497.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/iio/adc/ltc2497.c b/drivers/iio/adc/ltc2497.c
> index 17370c5..ec198c6 100644
> --- a/drivers/iio/adc/ltc2497.c
> +++ b/drivers/iio/adc/ltc2497.c
> @@ -28,7 +28,6 @@ struct ltc2497_driverdata {
> struct ltc2497core_driverdata common_ddata;
> struct i2c_client *client;
> u32 recv_size;
> - u32 sub_lsb;
> /*
> * DMA (thus cache coherency maintenance) may require the
> * transfer buffers to live in their own cache lines.
> @@ -65,10 +64,10 @@ static int ltc2497_result_and_measure(struct ltc2497core_driverdata *ddata,
> * equivalent to a sign extension.
> */
> if (st->recv_size == 3) {
> - *val = (get_unaligned_be24(st->data.d8) >> st->sub_lsb)
> + *val = (get_unaligned_be24(st->data.d8) >> 6)
> - BIT(ddata->chip_info->resolution + 1);
> } else {
> - *val = (be32_to_cpu(st->data.d32) >> st->sub_lsb)
> + *val = (be32_to_cpu(st->data.d32) >> 6)
> - BIT(ddata->chip_info->resolution + 1);
> }
>
> @@ -122,7 +121,6 @@ static int ltc2497_probe(struct i2c_client *client)
> st->common_ddata.chip_info = chip_info;
>
> resolution = chip_info->resolution;
> - st->sub_lsb = 31 - (resolution + 1);
> st->recv_size = BITS_TO_BYTES(resolution) + 1;
>
> return ltc2497core_probe(dev, indio_dev);