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

From: Renato Lui Geh
Date: Fri Jan 18 2019 - 15:19:51 EST

Next message: Andrew F. Davis: "Re: [PATCH 2/4] staging: android: ion: Restrict cache maintenance to dma mapped memory"
Previous message: Laura Abbott: "Re: [PATCH 00/14] Misc ION cleanups and adding unmapped heap"
Next in thread: Jonathan Cameron: "Re: [PATCH 1/2] staging: iio: ad7780: Add gain & filter gpio support"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

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@xxxxxx> 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@xxxxxxxxxx> 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@xxxxxx>
> > ---
> > 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, \
>
> --
> You received this message because you are subscribed to the Google Groups "Kernel USP" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to kernel-usp+unsubscribe@xxxxxxxxxxxxxxxxx
> To post to this group, send email to kernel-usp@xxxxxxxxxxxxxxxxx
> To view this discussion on the web visit https://groups.google.com/d/msgid/kernel-usp/1543490289.11186.22.camel%40analog.com.
> For more options, visit https://groups.google.com/d/optout.

Next message: Andrew F. Davis: "Re: [PATCH 2/4] staging: android: ion: Restrict cache maintenance to dma mapped memory"
Previous message: Laura Abbott: "Re: [PATCH 00/14] Misc ION cleanups and adding unmapped heap"
Next in thread: Jonathan Cameron: "Re: [PATCH 1/2] staging: iio: ad7780: Add gain & filter gpio support"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]