Re: [PATCH v2 3/8] iio: inkern: error out on unsupported offset type

[Jonathan Cameron <jic23@kernel.org>]

On Mon,  7 Jun 2021 10:47:13 -0400
Liam Beguin <liambeguin@gmail.com> wrote:

> From: Liam Beguin <lvb@xiphos.com>
> 
> iio_convert_raw_to_processed_unlocked() assumes the offset is an
> integer.
> Make that clear to the consumer by returning an error on unsupported
> offset types without breaking valid implicit truncations.
> 
> Signed-off-by: Liam Beguin <lvb@xiphos.com>
> ---
>  drivers/iio/inkern.c | 34 +++++++++++++++++++++++++++++-----
>  1 file changed, 29 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c
> index b69027690ed5..0b5667f22b1d 100644
> --- a/drivers/iio/inkern.c
> +++ b/drivers/iio/inkern.c
> @@ -578,13 +578,37 @@ EXPORT_SYMBOL_GPL(iio_read_channel_average_raw);
>  static int iio_convert_raw_to_processed_unlocked(struct iio_channel *chan,
>  	int raw, int *processed, unsigned int scale)
>  {
> -	int scale_type, scale_val, scale_val2, offset;
> +	int scale_type, scale_val, scale_val2;
> +	int offset_type, offset_val, offset_val2;
>  	s64 raw64 = raw;
> -	int ret;
>  
> -	ret = iio_channel_read(chan, &offset, NULL, IIO_CHAN_INFO_OFFSET);
> -	if (ret >= 0)
> -		raw64 += offset;
> +	offset_type = iio_channel_read(chan, &offset_val, &offset_val2,
> +				       IIO_CHAN_INFO_OFFSET);
> +	if (offset_type >= 0) {
> +		switch (offset_type) {
> +		case IIO_VAL_INT:
> +			break;
> +		case IIO_VAL_INT_PLUS_MICRO:
> +			if (offset_val2 > 1000)

What's the logic behind this one?  > 1000000
would be an interesting corner case, though I'm not sure we've ever
explicitly disallowed it before.

Why are we at 1000th of that for the check?

> +				return -EINVAL;
> +			break;
> +		case IIO_VAL_INT_PLUS_NANO:
> +			if (offset_val2 > 1000000)

Similar this is a bit odd.

> +				return -EINVAL;
> +		case IIO_VAL_FRACTIONAL:
> +			if (offset_val2 != 1)
> +				return -EINVAL;

We could be more flexible on this, but I don't recall any
channels using this so far.

> +			break;
> +		case IIO_VAL_FRACTIONAL_LOG2:
> +			if (offset_val2)
> +				return -EINVAL;

Same in this case.

> +			break;
> +		default:
> +			return -EINVAL;
> +		}
> +
> +		raw64 += offset_val;
> +	}
>  
>  	scale_type = iio_channel_read(chan, &scale_val, &scale_val2,
>  					IIO_CHAN_INFO_SCALE);