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From:   Renato Lui Geh <renatogeh@gmail.com>
Date:   Fri, 18 Jan 2019 18:19:40 -0200
To:     Jonathan Cameron <jic23@kernel.org>
Cc:     Giuliano Augusto Faulin Belinassi <giuliano.belinassi@usp.br>,
        StefanSerban.Popa@analog.com, alexandru.Ardelean@analog.com,
        lars@metafoo.de, knaack.h@gmx.de, Michael.Hennerich@analog.com,
        Renato Geh <renatogeh@gmail.com>, giuliano.belinassi@gmail.com,
        Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
        gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org,
        linux-iio@vger.kernel.org, devel@driverdev.osuosl.org,
        kernel-usp@googlegroups.com
Subject: Re: [PATCH 1/2] staging: iio: ad7780: Add gain & filter gpio support
Message-ID: <20190118201820.mlwxeso2odpecdsf@renatolg>
References: <cover.1543428366.git.giuliano.belinassi@usp.br>
 <231cbc909b892a0ebe172460d34e9eeb9cfa3003.1543428366.git.giuliano.belinassi@usp.br>
 <1543490289.11186.22.camel@analog.com>
 <CAEFO=4AQe0B0inmE=w2T+xaFkKgPwnHLP7XkT30TjFV_AEKGbg@mail.gmail.com>
 <20181201172341.4c353eae@archlinux>
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Hi,

Sorry for the (extremely) late reply.

Comments inline.

Renato

On 12/01, Jonathan Cameron wrote:
>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.

Why wouldn't the vref voltage not change after initialization? Shouldn't
we keep reading and updating this in read_raw?
>>
>> > 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.

Shouldn't we read vref inside read_raw in order to get up-to-date
readings on voltage values? Or should we keep reading from a cached
value?
>>
>> 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 see. I thought the filter input was in mHz. So should I compare
1000*val with AD7780_FILTER_MIDPOINT?
>
>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?

If I'm not mistaken, we had agreed earlier to remove this altogether, as
having a redundancy check could potentially slow down reading.
>>
>> 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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