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SubjectRe: [PATCH 06/11] staging: iio: adt7316: fix the dac write calculation
On Tue, 11 Dec 2018 17:54:58 -0700
Jeremy Fertic <jeremyfertic@gmail.com> wrote:

> The lsb calculation is not masking the correct bits from the user input.
> Subtract 1 from (1 << offset) to correctly set up the mask to be applied
> to user input.
>
> The lsb register stores its value starting at the bit 7 position.
> adt7316_store_DAC() currently assumes the value is at the other end of the
> register. Shift the lsb value before storing it in a new variable lsb_reg,
> and write this variable to the lsb register.
>
> Signed-off-by: Jeremy Fertic <jeremyfertic@gmail.com>
Looks right to me.

Wow this driver had some impressively wrong maths in it ;)
Glad you are fixing this up.

I'll pick up in v2.

Thanks,

Jonathan

> ---
> drivers/staging/iio/addac/adt7316.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/staging/iio/addac/adt7316.c b/drivers/staging/iio/addac/adt7316.c
> index b7d12d003ddc..77ef3c209b67 100644
> --- a/drivers/staging/iio/addac/adt7316.c
> +++ b/drivers/staging/iio/addac/adt7316.c
> @@ -1442,7 +1442,7 @@ static ssize_t adt7316_show_DAC(struct adt7316_chip_info *chip,
> static ssize_t adt7316_store_DAC(struct adt7316_chip_info *chip,
> int channel, const char *buf, size_t len)
> {
> - u8 msb, lsb, offset;
> + u8 msb, lsb, lsb_reg, offset;
> u16 data;
> int ret;
>
> @@ -1460,9 +1460,13 @@ static ssize_t adt7316_store_DAC(struct adt7316_chip_info *chip,
> return -EINVAL;
>
> if (chip->dac_bits > 8) {
> - lsb = data & (1 << offset);
> + lsb = data & ((1 << offset) - 1);
> + if (chip->dac_bits == 12)
> + lsb_reg = lsb << ADT7316_DA_12_BIT_LSB_SHIFT;
> + else
> + lsb_reg = lsb << ADT7316_DA_10_BIT_LSB_SHIFT;
> ret = chip->bus.write(chip->bus.client,
> - ADT7316_DA_DATA_BASE + channel * 2, lsb);
> + ADT7316_DA_DATA_BASE + channel * 2, lsb_reg);
> if (ret)
> return -EIO;
> }

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