Date: Fri, 8 Apr 2016 18:00:03 +0200 (CEST)
From: Peter Meerwald-Stadler <pmeerw@pmeerw.net>
To: Slawomir Stepien <sst@poczta.fm>
cc: jic23@kernel.org, knaack.h@gmx.de, lars@metafoo.de,
        linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] iio: potentiometer: add driver for Maxim Integrated
 DS1803
In-Reply-To: <20160408152817.GA2847@x220>
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References: <20160407165118.GA2333@x220> <alpine.DEB.2.02.1604072130040.26969@pmeerw.net> <20160408152817.GA2847@x220>
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> > maybe a #define to explain the name of register 0
> 
> Well this zero is not register nor any kind of command that DS1803 needs to send
> back pots values.
> DS1803 only requires the standard R/W bit to be set as read.
> I used _word_ function series to get back a word (16 bits) as this poti returns
> 16 bits.
> 
> How should I named it?
> 
> #define NON_COMMAND 0
> ?

maybe i2c_transfer() is more appropriate then

        u8 databuf[2];
        struct i2c_msg msgs[2] = {
                { .addr = client->addr, .len = sizeof(databuf), .buf = databuf,
                  .flags = I2C_M_RD } };
        ret = i2c_transfer(client->adapter, msgs, 2);

this does not send any data to the chip but only reads two bytes
 
> Or should I use different function? (2x i2c_smbus_read_byte?)
> 
> The i2c_smbus_read_byte() function also used 0 as command
> for its transfers...

> > > +static int ds1803_write_raw(struct iio_dev *indio_dev,
> > > +			     struct iio_chan_spec const *chan,
> > > +			     int val, int val2, long mask)
> > > +{
> > > +	struct ds1803_data *data = iio_priv(indio_dev);
> > > +	int pot = chan->channel;
> > > +
> > > +	switch (mask) {
> > > +	case IIO_CHAN_INFO_RAW:
> > > +		if (val > DS1803_MAX_POS || val < 0)
> > 
> > check that val2 is 0 or use .write_raw_get_fmt
> 
> At this point I do not know why should I do it, but I will look into that.

write_raw expects a VAL_INT_PLUS_MICROS per default, passed 
in val and val2

you can change that with .write_raw_get_fmt (e.g. to expect VAL_INT),
or just make sure that the micros are 0
 
-- 

Peter Meerwald-Stadler
+43-664-2444418 (mobile)