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Date: Mon, 6 May 2024 15:05:57 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Julien Stephan <jstephan@...libre.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>, Michael Hennerich
<Michael.Hennerich@...log.com>, Nuno Sá <nuno.sa@...log.com>,
David Lechner <dlechner@...libre.com>, Rob Herring <robh@...nel.org>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley
<conor+dt@...nel.org>, Liam Girdwood <lgirdwood@...il.com>, Mark Brown
<broonie@...nel.org>, kernel test robot <lkp@...el.com>,
linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v6 08/10] iio: adc: ad7380: add oversampling support
On Wed, 01 May 2024 16:55:41 +0200
Julien Stephan <jstephan@...libre.com> wrote:
> ad7380x(-4) parts are able to do oversampling to increase accuracy.
> They support 2 average modes: normal average and rolling overage.
> This commits focus on enabling normal average oversampling, which is the
> default one.
The other case got me curious. If you do want to support the rolling average
in future, it could probably be handled as a low pass filter control rather
than a form of oversampling. Anyhow, not relevant here!
>
> Normal averaging involves taking a number of samples, adding them together,
> and dividing the result by the number of samples taken.
> This result is then output from the device. The sample data is cleared when
> the process completes. Because we need more samples to output a value,
> the data output rate decrease with the oversampling ratio.
>
> Signed-off-by: Julien Stephan <jstephan@...libre.com>
Hi Julien.
A few additional comments inline.
Jonathan
> ---
> drivers/iio/adc/ad7380.c | 115 ++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 114 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/iio/adc/ad7380.c b/drivers/iio/adc/ad7380.c
> index 020959759170..1e3869f5e48c 100644
> --- a/drivers/iio/adc/ad7380.c
> +++ b/drivers/iio/adc/ad7380.c
> @@ -88,7 +88,10 @@ struct ad7380_chip_info {
> .type = IIO_VOLTAGE, \
> .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | \
> ((diff) ? 0 : BIT(IIO_CHAN_INFO_OFFSET)), \
> - .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE), \
> + .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) | \
> + BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO), \
> + .info_mask_shared_by_type_available = \
> + BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO), \
> .indexed = 1, \
> .differential = (diff), \
> .channel = (diff) ? (2 * (index)) : (index), \
> @@ -156,6 +159,16 @@ static const struct ad7380_timing_specs ad7380_4_timing = {
> .t_csh_ns = 20,
> };
>
> +/*
> + * Available oversampling ratios. The indices correspond
> + * with the bit value expected by the chip.
> + * The available ratios depend on the averaging mode,
> + * only normal averaging is supported for now
> + */
> +static const int ad7380_normal_average_oversampling_ratios[] = {
> + 1, 2, 4, 8, 16, 32,
> +};
> +
> static const struct ad7380_chip_info ad7380_chip_info = {
> .name = "ad7380",
> .channels = ad7380_channels,
> @@ -231,6 +244,7 @@ static const struct ad7380_chip_info ad7384_4_chip_info = {
> struct ad7380_state {
> const struct ad7380_chip_info *chip_info;
> struct spi_device *spi;
> + unsigned int oversampling_ratio;
> struct regmap *regmap;
> unsigned int vref_mv;
> unsigned int vcm_mv[MAX_NUM_CHANNELS];
> @@ -386,6 +400,12 @@ static int ad7380_read_direct(struct ad7380_state *st,
> };
> int ret;
>
> + /*
> + * In normal average oversampling we need to wait for multiple conversions to be done
Wrap comment at 80 chars. Generally I prefer we keep to old limit of 80 unless
there is a readability advantage. I don't see such an advantage in this case.
> + */
> + if (st->oversampling_ratio > 1)
> + xfers[0].delay.value = T_CONVERT_NS + 500 * st->oversampling_ratio;
> +
> +
> +/**
> + * check_osr - Check the oversampling ratio
> + * @available_ratio: available ratios's array
> + * @size: size of the available_ratio array
> + * ratio: ratio to check
> + *
> + * Check if ratio is present in @available_ratio. Check for exact match.
> + * @available_ratio is an array of the available ratios (depending on the oversampling mode).
> + * The indices must correspond with the bit value expected by the chip.
> + */
> +static inline int check_osr(const int *available_ratio, int size, int ratio)
> +{
> + int i;
> +
> + for (i = 0; i < size; i++) {
> + if (ratio == available_ratio[i])
> + return i;
> + }
> +
> + return -EINVAL;
> +}
> +
> +static int ad7380_write_raw(struct iio_dev *indio_dev,
> + struct iio_chan_spec const *chan, int val,
> + int val2, long mask)
> +{
> + struct ad7380_state *st = iio_priv(indio_dev);
> + int ret, osr;
> +
> + switch (mask) {
> + case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> + osr = check_osr(ad7380_normal_average_oversampling_ratios,
Nuno already pointed out function name should be prefixed.
> + ARRAY_SIZE(ad7380_normal_average_oversampling_ratios),
> + val);
If this is just checking, why does it return osr? Feels like name needs
to be ad7380_osr_to_regval() or something like that.
> +
> + if (osr < 0)
> + return osr;
> +
> + iio_device_claim_direct_scoped(return -EBUSY, indio_dev) {
> + ret = regmap_update_bits(st->regmap, AD7380_REG_ADDR_CONFIG1,
> + AD7380_CONFIG1_OSR,
> + FIELD_PREP(AD7380_CONFIG1_OSR, osr));
> +
> + if (ret)
> + return ret;
> +
> + st->oversampling_ratio = val;
> +
> + /*
> + * Perform a soft reset.
> + * This will flush the oversampling block and FIFO but will
> + * maintain the content of the configurable registers.
> + */
> + ret = regmap_update_bits(st->regmap, AD7380_REG_ADDR_CONFIG2,
> + AD7380_CONFIG2_RESET,
> + FIELD_PREP(AD7380_CONFIG2_RESET,
> + AD7380_CONFIG2_RESET_SOFT));
> + }
> + return 0;
> default:
> return -EINVAL;
> }
> @@ -435,6 +540,8 @@ static int ad7380_read_raw(struct iio_dev *indio_dev,
>
> static const struct iio_info ad7380_info = {
> .read_raw = &ad7380_read_raw,
> + .read_avail = &ad7380_read_avail,
> + .write_raw = &ad7380_write_raw,
> .debugfs_reg_access = &ad7380_debugfs_reg_access,
> };
>
> @@ -458,6 +565,12 @@ static int ad7380_init(struct ad7380_state *st, struct regulator *vref)
> if (ret < 0)
> return ret;
>
> + /* Disable oversampling by default.
IIO comment syntax is
/*
* Disable oversampling by default.
Also, curiously short lines that could definitely be wrapped nearer 80 chars!
> + * This is the default value after reset,
> + * so just initialize internal data
> + */
> + st->oversampling_ratio = 1;
> +
> /* SPI 1-wire mode */
> return regmap_update_bits(st->regmap, AD7380_REG_ADDR_CONFIG2,
> AD7380_CONFIG2_SDO,
>
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