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

Renato Lui Geh
2019-01-18T20:19:50Z

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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