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SubjectRe: [PATCH v4 5/6] iio:adxl372: Add sampling frequency support
Hi Stefan,

On Mon, Aug 06, 2018 at 03:04:46PM +0300, Stefan Popa wrote:
> This patch adds the option for the user to select the sampling frequency.
> Also, the user can read the available frequencies and read the currently
> set frequency via the read_raw function. The frequency can be set via the
> write_raw function.
>
> When the frequency is set, the bandwidth is also checked and ensured
> that it is constrained to at most half of the sampling frequency. Also, the
> activity and inactivity timers have to be updated because they depend on
> the selected ODR.
>
> Signed-off-by: Stefan Popa <stefan.popa@analog.com>
> ---
> drivers/iio/accel/adxl372.c | 74 ++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 73 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/iio/accel/adxl372.c b/drivers/iio/accel/adxl372.c
> index 623c32d..d991d1c 100644
> --- a/drivers/iio/accel/adxl372.c
> +++ b/drivers/iio/accel/adxl372.c
> @@ -223,7 +223,8 @@ static const struct adxl372_axis_lookup adxl372_axis_lookup_table[] = {
> .modified = 1, \
> .channel2 = IIO_MOD_##axis, \
> .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), \
> - .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE), \
> + .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) | \
> + BIT(IIO_CHAN_INFO_SAMP_FREQ), \
> .scan_index = index, \
> .scan_type = { \
> .sign = 's', \
> @@ -311,6 +312,19 @@ static int adxl372_set_odr(struct adxl372_state *st,
> return ret;
> }
>
> +static int adxl372_find_closest_match(const int *array,
> + unsigned int size, int val)
> +{
> + int i;
> +
> + for (i = 0; i < size; i++) {
> + if (val <= array[i])
> + return i;
> + }
> +
> + return size - 1;
> +}

Hum, would find_closest() work for this?
See include/linux/util_macros.h

> +
> static int adxl372_set_bandwidth(struct adxl372_state *st,
> enum adxl372_bandwidth bw)
> {
> @@ -631,6 +645,51 @@ static int adxl372_read_raw(struct iio_dev *indio_dev,
> *val = 0;
> *val2 = ADXL372_USCALE;
> return IIO_VAL_INT_PLUS_MICRO;
> + case IIO_CHAN_INFO_SAMP_FREQ:
> + *val = adxl372_samp_freq_tbl[st->odr];
> + return IIO_VAL_INT;
> + }
> +
> + return -EINVAL;
> +}
> +
> +static int adxl372_write_raw(struct iio_dev *indio_dev,
> + struct iio_chan_spec const *chan,
> + int val, int val2, long info)
> +{
> + struct adxl372_state *st = iio_priv(indio_dev);
> + int odr_index, ret;
> +

Is it worth to make sure that val2 is zero here?

> + switch (info) {
> + case IIO_CHAN_INFO_SAMP_FREQ:
> + odr_index = adxl372_find_closest_match(adxl372_samp_freq_tbl,
> + ARRAY_SIZE(adxl372_samp_freq_tbl),
> + val);
> + ret = adxl372_set_odr(st, odr_index);
> + if (ret < 0)
> + return ret;
> + /*
> + * The timer period depends on the ODR selected.
> + * At 3200 Hz and below, it is 6.6 ms; at 6400 Hz, it is 3.3 ms
> + */
> + ret = adxl372_set_activity_time_ms(st, st->act_time_ms);
> + if (ret < 0)
> + return ret;
> + /*
> + * The timer period depends on the ODR selected.
> + * At 3200 Hz and below, it is 26 ms; at 6400 Hz, it is 13 ms
> + */
> + ret = adxl372_set_inactivity_time_ms(st, st->inact_time_ms);
> + if (ret < 0)
> + return ret;
> + /*
> + * The maximum bandwidth is constrained to at most half of
> + * the ODR to ensure that the Nyquist criteria is not violated
> + */
> + if (st->bw > odr_index)
> + ret = adxl372_set_bandwidth(st, odr_index);
> +
> + return ret;
> default:
> return -EINVAL;
> }
> @@ -763,8 +822,21 @@ static const struct iio_trigger_ops adxl372_trigger_ops = {
> .set_trigger_state = adxl372_dready_trig_set_state,
> };
>
> +static IIO_CONST_ATTR_SAMP_FREQ_AVAIL("400 800 1600 3200 6400");
> +
> +static struct attribute *adxl372_attributes[] = {
> + &iio_const_attr_sampling_frequency_available.dev_attr.attr,
> + NULL,
> +};
> +
> +static const struct attribute_group adxl372_attrs_group = {
> + .attrs = adxl372_attributes,
> +};
> +
> static const struct iio_info adxl372_info = {
> + .attrs = &adxl372_attrs_group,
> .read_raw = adxl372_read_raw,
> + .write_raw = adxl372_write_raw,
> .debugfs_reg_access = &adxl372_reg_access,
> .hwfifo_set_watermark = adxl372_set_watermark,
> };
> --
> 2.7.4


Best regards,
Marcus Folkesson
>
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