staging: iio: ad7780: correct driver read

The purpose of this series is to correct two issues in the driver's raw read function.

Changelog:
* v2

	- separated original patch into two patches
	  (https://marc.info/?l=linux-iio&m=154047435605492)

Renato Lui Geh (2):
staging: iio: ad7780: update voltage on read
staging: iio: ad7780: fix offset read value

drivers/staging/iio/adc/ad7780.c | 6 +++++-

1 file changed, 5 insertions(+), 1 deletion(-)

2.19.1

The ad7780 driver previously did not read the correct device output, as it read an outdated value set at initialization. It now updates its voltage on read.

---
drivers/staging/iio/adc/ad7780.c | 4 ++++

1 file changed, 4 insertions(+)

index b67412db0318..27972563bb6a 100644
@@ -87,11 +87,15 @@ static int ad7780_read_raw(struct iio_dev *indio_dev,

long m)

{
	struct ad7780_state *st = iio_priv(indio_dev);

+ int voltage_uv = 0;

	switch (m) {
	case IIO_CHAN_INFO_RAW:
		return ad_sigma_delta_single_conversion(indio_dev, chan, val);
	case IIO_CHAN_INFO_SCALE:
+		voltage_uv = regulator_get_voltage(st->reg);
+		if (voltage_uv)
+			st->int_vref_mv = voltage_uv/1000;
		*val = st->int_vref_mv * st->gain;
		*val2 = chan->scan_type.realbits - 1;
		return IIO_VAL_FRACTIONAL_LOG2;

2.19.1

Variable val subtracted an uninitialized value on IIO_CHAN_INFO_OFFSET. This was fixed by assigning the correct value instead.

---
drivers/staging/iio/adc/ad7780.c | 2 +-

1 file changed, 1 insertion(+), 1 deletion(-)

index 27972563bb6a..06700fe554a2 100644
@@ -100,7 +100,7 @@ static int ad7780_read_raw(struct iio_dev *indio_dev,

		*val2 = chan->scan_type.realbits - 1;
		return IIO_VAL_FRACTIONAL_LOG2;
	case IIO_CHAN_INFO_OFFSET:
-		*val -= (1 << (chan->scan_type.realbits - 1));
+		*val = -(1 << (chan->scan_type.realbits - 1));
		return IIO_VAL_INT;
	}

2.19.1

It obviously doesn't make much difference, but as you are respinning anyway... Please could you always put fixes at the beginning of a set as it makes it easier to back port them. It think this one is simple enough that it is worth applying to the stable kernels.

(naturally I could do that anyway as the rebase is trivial, so I'm just encouraging good practice by asking you to do it in v3!)

Thanks,

Jonathan

Hi Jonathan,

Thank you for the review.

From probe:

if (voltage_uv)

	st->int_vref_mv = voltage_uv / 1000;
else
	dev_warn(&spi->dev, "Reference voltage unspecified\n");

So the idea was to, when voltage_uv = 0, return the previous voltage. Should I instead handle this as an error the same way as in probe?

Thanks,
Renato

I would return it as an error. I can't really see how we would get this to occur if the bindings are all correct and appropriate driver support is there for the regulator to actually let us use it.

If we wanted to handle the case of no regulator having been provided cleanly then we should it using an optional regulator get, and not provide the scale attribute at all if we can't know what it will read. This is a weird enough corner case though that I just wouldn't bother handling it as anything other than an error.

Thanks,

Jonathan