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SubjectRe: [PATCH v2 1/6] iio: accel: adxl372: Add support for FIFO peak mode
On Tue, 25 Feb 2020 14:09:04 +0200
Alexandru Tachici <alexandru.tachici@analog.com> wrote:

> From: Stefan Popa <stefan.popa@analog.com>
>
> By default, if all three channels (x, y, z) are enabled, sample sets of
> concurrent 3-axis data is stored in the FIFO. This patch adds the option
> to configure the FIFO to store peak acceleration (x, y and z) of every
> over-threshold event. Since we cannot store 1 or 2 axis peak acceleration
> data in the FIFO, then all three axis need to be enabled in order for this
> mode to work.
>
> Signed-off-by: Stefan Popa <stefan.popa@analog.com>

First apologies this was one of the sets that I didn't get to last week.

This is a bit of an odd one, but I suppose the general approach is fine.

A few questions on specifics inline.

> ---
> drivers/iio/accel/adxl372.c | 46 +++++++++++++++++++++++++++++++++++++
> 1 file changed, 46 insertions(+)
>
> diff --git a/drivers/iio/accel/adxl372.c b/drivers/iio/accel/adxl372.c
> index 67b8817995c0..ed93534f8dba 100644
> --- a/drivers/iio/accel/adxl372.c
> +++ b/drivers/iio/accel/adxl372.c
> @@ -264,6 +264,7 @@ struct adxl372_state {
> u8 int2_bitmask;
> u16 watermark;
> __be16 fifo_buf[ADXL372_FIFO_SIZE];
> + bool peak_fifo_mode_en;
> };
>
> static const unsigned long adxl372_channel_masks[] = {
> @@ -722,6 +723,40 @@ static int adxl372_write_raw(struct iio_dev *indio_dev,
> }
> }
>
> +static ssize_t adxl372_peak_fifo_en_get(struct device *dev,
> + struct device_attribute *attr,
> + char *buf)
> +{
> + struct adxl372_state *st = iio_priv(dev_to_iio_dev(dev));
> +
> + return sprintf(buf, "%d\n", st->peak_fifo_mode_en);
> +}
> +
> +static ssize_t adxl372_peak_fifo_en_set(struct device *dev,
> + struct device_attribute *attr,
> + const char *buf, size_t len)
> +{
> + struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> + struct adxl372_state *st = iio_priv(indio_dev);
> + bool val;
> + int ret;
> +
> + if (iio_buffer_enabled(indio_dev))
> + return -EBUSY;

Prefer if you use the iio_claim_direct_mode to ensure we are in
non buffered mode until we reach a consistent state. Then set
the variable and release direct mode.

Otherwise you might have a race between a write
to this and enabling the buffered mode.

> +
> + ret = kstrtobool(buf, &val);
> + if (ret)
> + return ret;
> +
> + st->peak_fifo_mode_en = val;
> +
> + return len;
> +}
> +
> +static IIO_DEVICE_ATTR(buffer_peak_mode_enable, 0644,
> + adxl372_peak_fifo_en_get,
> + adxl372_peak_fifo_en_set, 0);
> +
> static ssize_t adxl372_show_filter_freq_avail(struct device *dev,
> struct device_attribute *attr,
> char *buf)
> @@ -817,11 +852,21 @@ static int adxl372_buffer_postenable(struct iio_dev *indio_dev)
> st->fifo_format = adxl372_axis_lookup_table[i].fifo_format;
> st->fifo_set_size = bitmap_weight(indio_dev->active_scan_mask,
> indio_dev->masklength);
> +
> + /* Configure the FIFO to store sets of impact event peak. */
> + if (st->peak_fifo_mode_en) {
> + st->fifo_format = ADXL372_XYZ_PEAK_FIFO;
> + if (st->fifo_set_size != 3)
> + dev_warn(&indio_dev->dev,
> + "All axis must be enabled in peak mode.");

What happens otherwise? Real question is should this just be an error and
result in us dropping out of buffered mode again? How would a userspace
program that had hit this know there was an issue?

> + }
> +
> /*
> * The 512 FIFO samples can be allotted in several ways, such as:
> * 170 sample sets of concurrent 3-axis data
> * 256 sample sets of concurrent 2-axis data (user selectable)
> * 512 sample sets of single-axis data
> + * 170 sets of impact event peak (x, y, z)
> */
> if ((st->watermark * st->fifo_set_size) > ADXL372_FIFO_SIZE)
> st->watermark = (ADXL372_FIFO_SIZE / st->fifo_set_size);
> @@ -894,6 +939,7 @@ static IIO_DEVICE_ATTR(in_accel_filter_low_pass_3db_frequency_available,
> static struct attribute *adxl372_attributes[] = {
> &iio_const_attr_sampling_frequency_available.dev_attr.attr,
> &iio_dev_attr_in_accel_filter_low_pass_3db_frequency_available.dev_attr.attr,
> + &iio_dev_attr_buffer_peak_mode_enable.dev_attr.attr,
> NULL,
> };
>

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