Re: [PATCH 1/2] staging: iio: ad7780: Add gain & filter gpio support

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 29 Nov 2018 11:02:46 -0200
Giuliano Augusto Faulin Belinassi <giuliano.belinassi@usp.br> wrote:

> Hi

A few follow ups from me having read the result in patch 2.

Jonathan
> 
> On Thu, Nov 29, 2018 at 9:18 AM Popa, Stefan Serban
> <StefanSerban.Popa@analog.com> wrote:
> >
> > On Mi, 2018-11-28 at 16:15 -0200, Giuliano Belinassi wrote:  
> > > Previously, the AD7780 driver only supported gpio for the 'powerdown'
> > > pin. This commit adds suppport for the 'gain' and 'filter' pin.
> > >
> > > Signed-off-by: Giuliano Belinassi <giuliano.belinassi@usp.br>
> > > ---
> > > Changes in v2:
> > >     - Now this patch is part of the patchset that aims to remove ad7780
> > > out of staging. https://marc.info/?l=linux-iio&m=154282349808890&w=2
> > >     - Also, now it reads voltage and filter values from the userspace
> > > instead of gpio pin states.  
> >
> > Hello,
> > Please see bellow.
> >  
> > >
> > >  drivers/staging/iio/adc/ad7780.c       | 78 ++++++++++++++++++++++++--
> > >  include/linux/iio/adc/ad_sigma_delta.h |  5 ++
> > >  2 files changed, 79 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/staging/iio/adc/ad7780.c
> > > b/drivers/staging/iio/adc/ad7780.c
> > > index c4a85789c2db..05979a79fda3 100644
> > > --- a/drivers/staging/iio/adc/ad7780.c
> > > +++ b/drivers/staging/iio/adc/ad7780.c
> > > @@ -39,6 +39,12 @@
> > >  #define AD7170_PATTERN               (AD7780_PAT0 | AD7170_PAT2)
> > >  #define AD7170_PATTERN_MASK  (AD7780_PAT0 | AD7780_PAT1 |
> > > AD7170_PAT2)
> > >
> > > +#define AD7780_GAIN_GPIO     0
> > > +#define AD7780_FILTER_GPIO   1
> > > +
> > > +#define AD7780_GAIN_MIDPOINT 64
> > > +#define AD7780_FILTER_MIDPOINT       13350
> > > +
> > >  struct ad7780_chip_info {
> > >       struct iio_chan_spec    channel;
> > >       unsigned int            pattern_mask;
> > > @@ -50,6 +56,8 @@ struct ad7780_state {
> > >       const struct ad7780_chip_info   *chip_info;
> > >       struct regulator                *reg;
> > >       struct gpio_desc                *powerdown_gpio;
> > > +     struct gpio_desc                *gain_gpio;
> > > +     struct gpio_desc                *filter_gpio;
> > >       unsigned int    gain;
> > >
> > >       struct ad_sigma_delta sd;
> > > @@ -115,18 +123,65 @@ static int ad7780_read_raw(struct iio_dev
> > > *indio_dev,
> > >       return -EINVAL;
> > >  }
> > >
> > > +static int ad7780_write_raw(struct iio_dev *indio_dev,
> > > +                         struct iio_chan_spec const *chan,
> > > +                         int val,
> > > +                         int val2,
> > > +                         long m)
> > > +{
> > > +     struct ad7780_state *st = iio_priv(indio_dev);
> > > +     const struct ad7780_chip_info *chip_info = st->chip_info;
> > > +     int uvref, gain;
> > > +     unsigned int full_scale;
> > > +
> > > +     if (!chip_info->is_ad778x)
> > > +             return 0;
> > > +
> > > +     switch (m) {
> > > +     case IIO_CHAN_INFO_SCALE:
> > > +             if (val != 0)
> > > +                     return -EINVAL;
> > > +
> > > +             uvref = regulator_get_voltage(st->reg);  
> >
> > regulator_get_voltage() has already been called in the probe function and
> > the result is stored in st->int_vref_mv.  
> 
> This was removed in commit  9eae69ddbc4717a0bd702eddac76c7848773bf71
> because the value was not being updated. But I agree if the vref
> voltage is not going to change at all after the initialization, then
> this value should be kept in memory.
> 
> > My suggestion would be to use a local vref variable declared as unsigned
> > int. It is my fault that I haven't explained correctly in the previous
> > email, but you need to multiply vref_mv with 1000000LL in order to get the
> > right precision: vref = st->int_vref_mv * 1000000LL. Afterwards you will be
> > able to perform the divisions.  
> 
> Thanks for this info! :-)
> Shouldn't we store this in uV (microVolts)? This will yield a more
> accurate result after the multiplication.
> 
> > > +
> > > +             if (uvref < 0)
> > > +                     return uvref;
> > > +
> > > +             full_scale = 1 << (chip_info->channel.scan_type.realbits
> > > - 1);
> > > +             gain = DIV_ROUND_CLOSEST(uvref, full_scale);
> > > +             gain = DIV_ROUND_CLOSEST(gain, val2);
> > > +
> > > +             gpiod_set_value(st->gain_gpio, gain <
> > > AD7780_GAIN_MIDPOINT ? 0 : 1);  
> >
> > Once the gain is set, you can store it in st->gain variable.  
> 
> Yes, we forgot it.
> 
> >  
> > > +     case IIO_CHAN_INFO_SAMP_FREQ:
> > > +             if (val2 != 0)
> > > +                     return -EINVAL;
comment I raised in patch 2 about the odd preciseness of insisting
no decimal places, but matching any value based on a threshold on the
whole number part.

I'd also expect to see read_raw support for this.

> > > +
> > > +             gpiod_set_value(st->filter_gpio, val <
> > > AD7780_FILTER_MIDPOINT ? 0 : 1);  
> >
> > This is probably fine, although I am not a big fan of the ternary operator.
> > A simple if else statement would do. However, I don't feel strongly about
> > it, so feel free to disagree.
> >  
> > > +     break;
> > > +     }
> > > +
> > > +     return 0;
> > > +}
> > > +
> > >  static int ad7780_postprocess_sample(struct ad_sigma_delta *sigma_delta,
> > >                                    unsigned int raw_sample)
> > >  {
> > >       struct ad7780_state *st = ad_sigma_delta_to_ad7780(sigma_delta);
> > >       const struct ad7780_chip_info *chip_info = st->chip_info;
> > > +     int val;
> > >
> > >       if ((raw_sample & AD7780_ERR) ||
> > >           ((raw_sample & chip_info->pattern_mask) != chip_info-  
> > > >pattern))  
> > >               return -EIO;
> > >
> > >       if (chip_info->is_ad778x) {
> > > -             if (raw_sample & AD7780_GAIN)
> > > +             val = raw_sample & AD7780_GAIN;
> > > +
> > > +             if (val != gpiod_get_value(st->gain_gpio))
> > > +                     return -EIO;  
> >
> > It is not obvious to me what is the point of this check. Maybe you can add
> > a comment?  
> 
> It seems to be a redundancy check. It is getting the 32-bits
> raw_output, getting the bit that represents the GAIN value and
> checking if the pin is set accordingly (see Figure 22 of datasheet,
> page 13). Is this correct? If yes we add a comment explaining this.
> 
> >  
> > > +
> > > +             if (val)
> > >                       st->gain = 1;
> > >               else
> > >                       st->gain = 128;  
> >
> > Do we still need this? I am not convinced.  
> No, I don't think so. Thanks for pointing this out :-)
> 
> >  
> > > @@ -141,18 +196,20 @@ static const struct ad_sigma_delta_info
> > > ad7780_sigma_delta_info = {
> > >       .has_registers = false,
> > >  };
> > >
> > > -#define AD7780_CHANNEL(bits, wordsize) \
> > > +#define AD7170_CHANNEL(bits, wordsize) \
> > >       AD_SD_CHANNEL_NO_SAMP_FREQ(1, 0, 0, bits, 32, wordsize - bits)
> > > +#define AD7780_CHANNEL(bits, wordsize) \
> > > +     AD_SD_CHANNEL_GAIN_FILTER(1, 0, 0, bits, 32, wordsize - bits)
> > >
> > >  static const struct ad7780_chip_info ad7780_chip_info_tbl[] = {
> > >       [ID_AD7170] = {
> > > -             .channel = AD7780_CHANNEL(12, 24),
> > > +             .channel = AD7170_CHANNEL(12, 24),
> > >               .pattern = AD7170_PATTERN,
> > >               .pattern_mask = AD7170_PATTERN_MASK,
> > >               .is_ad778x = false,
> > >       },
> > >       [ID_AD7171] = {
> > > -             .channel = AD7780_CHANNEL(16, 24),
> > > +             .channel = AD7170_CHANNEL(16, 24),
> > >               .pattern = AD7170_PATTERN,
> > >               .pattern_mask = AD7170_PATTERN_MASK,
> > >               .is_ad778x = false,
> > > @@ -173,6 +230,7 @@ static const struct ad7780_chip_info
> > > ad7780_chip_info_tbl[] = {
> > >
> > >  static const struct iio_info ad7780_info = {
> > >       .read_raw = ad7780_read_raw,
> > > +     .write_raw = ad7780_write_raw,
> > >  };
> > >
> > >  static int ad7780_probe(struct spi_device *spi)
> > > @@ -222,6 +280,18 @@ static int ad7780_probe(struct spi_device *spi)
> > >               goto error_disable_reg;
> > >       }
> > >
> > > +     if (st->chip_info->is_ad778x) {
> > > +             st->gain_gpio = devm_gpiod_get_optional(&spi->dev,
> > > +                                                     "gain",
> > > +                                                     GPIOD_OUT_HIGH);
> > > +             if (IS_ERR(st->gain_gpio)) {  
> >
> > if the GPIO is optional, then we should continue in case of -ENODEV.
> >
> > Shouldn't we have a devm_gpiod_get_optional() call also for filter_gpio?
I had to check this one...

 * This is equivalent to gpiod_get(), except that when no GPIO was assigned to
 * the requested function it will return NULL. This is convenient for drivers
 * that need to handle optional GPIOs.

So nope, it shouldn't return -ENODEV;  unlike the clock equivalent which
IIRC does...

> >  
> > > +                     ret = PTR_ERR(st->gain_gpio);
> > > +                     dev_err(&spi->dev, "Failed to request gain GPIO:
> > > %d\n",
> > > +                             ret);
> > > +                     goto error_disable_reg;
> > > +             }
> > > +     }
> > > +
> > >       ret = ad_sd_setup_buffer_and_trigger(indio_dev);
> > >       if (ret)
> > >               goto error_disable_reg;
> > > diff --git a/include/linux/iio/adc/ad_sigma_delta.h
> > > b/include/linux/iio/adc/ad_sigma_delta.h
> > > index 730ead1a46df..6cadab6fd5fd 100644
> > > --- a/include/linux/iio/adc/ad_sigma_delta.h
> > > +++ b/include/linux/iio/adc/ad_sigma_delta.h
> > > @@ -173,6 +173,11 @@ int ad_sd_validate_trigger(struct iio_dev
> > > *indio_dev, struct iio_trigger *trig);
> > >       __AD_SD_CHANNEL(_si, _channel, -1, _address, _bits, \
> > >               _storagebits, _shift, NULL, IIO_VOLTAGE, 0)
> > >
> > > +#define AD_SD_CHANNEL_GAIN_FILTER(_si, _channel, _address, _bits, \
> > > +     _storagebits, _shift) \
> > > +     __AD_SD_CHANNEL(_si, _channel, -1, _address, _bits, \
> > > +             _storagebits, _shift, NULL, IIO_VOLTAGE,
> > > BIT(IIO_CHAN_INFO_RAW))
> > > +
> > >  #define AD_SD_TEMP_CHANNEL(_si, _address, _bits, _storagebits, _shift) \
> > >       __AD_SD_CHANNEL(_si, 0, -1, _address, _bits, \
> > >               _storagebits, _shift, NULL, IIO_TEMP, \  
> >
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