[PATCH 2/4] staging:iio:dac:ad5791: Allow asymmetrical reference voltages

[Jonathan Cameron]

Lars-Peter Clausen <lars at metafoo.de> wrote:

>On 10/19/2011 11:04 PM, Dan Carpenter wrote:
>> On Wed, Oct 19, 2011 at 05:47:50PM +0200, Lars-Peter Clausen wrote:
>>> @@ -225,6 +226,7 @@ static int ad5791_read_raw(struct iio_dev
>*indio_dev,
>>>  			   long m)
>>>  {
>>>  	struct ad5791_state *st = iio_priv(indio_dev);
>>> +	u64 val64;
>>>  	int ret;
>>>  
>>>  	switch (m) {
>>> @@ -234,12 +236,16 @@ static int ad5791_read_raw(struct iio_dev
>*indio_dev,
>>>  			return ret;
>>>  		*val &= AD5791_DAC_MASK;
>>>  		*val >>= chan->scan_type.shift;
>>> -		*val -= (1 << (chan->scan_type.realbits - 1));
>>>  		return IIO_VAL_INT;
>>>  	case (1 << IIO_CHAN_INFO_SCALE_SHARED):
>>>  		*val = 0;
>>>  		*val2 = (st->vref_mv * 1000) >> chan->scan_type.realbits;
>>>  		return IIO_VAL_INT_PLUS_MICRO;
>>> +	case (1 << IIO_CHAN_INFO_OFFSET_SHARED):
>>> +		val64 = (((u64)st->vref_neg_mv) << chan->scan_type.realbits);
>>> +		do_div(val64, st->vref_mv);
>>> +		*val = -val64;
>>> +		return IIO_VAL_INT;
>> 
>> Why does iio use switch over a bitfield?  If the values are mutually
>> exclusive then why not just use an enum?
>> 
>
>I wondered the very same and couldn't find a good explanation. I wanted
>to
>write a small RFC today converting the core and maybe 2-3 drivers to
>use the
>unshifted variants to see what Jonathan thinks about it.
It is legacy cruft from a while back. So I would be happy to see it go.
>
>> Hm...  "m" stands for mask and it gets created using the
>> IIO_UNMOD_EVENT_CODE() macro or sometimes it's just one bit at a
>> time copied from &chan->info_mask...  Odd.
>> 
>
>IIO_UNMOD_EVENT_CODE is only used for events which use a different
>callback
>function, so for the read_raw/write_raw callbacks we currently only
>ever
>pass one channel info type at a time.
>
>- Lars
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