Re: [PATCH v2] iio: adc: New driver for TI ADS7950 chips

[David Lechner]

On 11/22/2016 01:23 AM, Jonathan Cameron wrote:
> On 21 November 2016 22:54:24 GMT+00:00, Peter Meerwald-Stadler <pmeerw@xxxxxxxxxx> wrote:
> > > > +static int ti_ads7950_read_raw(struct iio_dev *indio_dev,
> > > > +			       struct iio_chan_spec const *chan,
> > > > +			       int *val, int *val2, long m)
> > > > +{
> > > > +	struct ti_ads7950_state *st = iio_priv(indio_dev);
> > > > +	int ret;
> > > > +
> > > > +	switch (m) {
> > > > +	case IIO_CHAN_INFO_RAW:
> > > > +
> > > > +		ret = iio_device_claim_direct_mode(indio_dev);
> > > > +		if (ret < 0)
> > > > +			return ret;
> > > > +
> > > > +		ret = ti_ads7950_scan_direct(st, chan->address);
> > > > +		iio_device_release_direct_mode(indio_dev);
> > > > +		if (ret < 0)
> > > > +			return ret;
> > > > +
> > > > +		if (chan->address != TI_ADS7950_EXTRACT(ret, 12, 4))
> > > > +			return -EIO;
> > > > +
> > > > +		*val = TI_ADS7950_EXTRACT(ret, 0, 12);
> > >
> > > I'm not sure if I am doing this right. There are 8- 10- and 12-bit
> > versions of
> > > this chip. The 8- and 10-bit versions still return a 12-bit number
> > where the
> > > last 4 or 2 bits are always 0. Should I be shifting the 12-bit value
> > here
> > > based on the chip being used so that *val is 0-255 for 8-bit and
> > 0-1023 for
> > > 10-bit? Or should this be *really* raw and not even use
> > TI_ADS7950_EXTRACT()
> > > to mask the channel address bits?
> >
> > I'd shift and adjust _SCALE so that *val * scale gives mV
> It would also be fine to not do anything and let userspace deal with shifting and masking for
> buffered data.  Non buffered obviously still needs shifting and masking though!

I have sent a v3 patch already that does exactly this. Buffered data is 
untouched and unbuffered data is now correct with shifting and masking.

> I'd slightly prefer the doing nothing route but don't really care as both are valid uses of the ABI.
>
> Jonathan
> > > > +
> > > > +		return IIO_VAL_INT;
> > > > +	case IIO_CHAN_INFO_SCALE:
> > > > +		ret = ti_ads7950_get_range(st);
> > > > +		if (ret < 0)
> > > > +			return ret;
> > > > +
> > > > +		*val = ret;
> > > > +		*val2 = chan->scan_type.realbits;
> > > > +
> > > > +		return IIO_VAL_FRACTIONAL_LOG2;
> > > > +	}
> > > > +
> > > > +	return -EINVAL;
> > > > +}