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

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Date:   Tue, 22 Nov 2016 12:23:46 -0600
From:   David Lechner <david@...hnology.com>
To:     Jonathan Cameron <jic23@...23.retrosnub.co.uk>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org
Subject: Re: [PATCH v2] iio: adc: New driver for TI ADS7950 chips

On 11/22/2016 01:23 AM, Jonathan Cameron wrote:
>
>
> On 21 November 2016 22:54:24 GMT+00:00, Peter Meerwald-Stadler <pmeerw@...erw.net> 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;
>>>> +}
>