Re: [PATCH v3 13/15] iio: accel: adxl345: add inactivity feature

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 20 Feb 2025 10:42:32 +0000
Lothar Rubusch <l.rubusch@gmail.com> wrote:

> Add the inactivity feature of the sensor. When activity and inactivity
> are enabled, a link bit will be set linking activity and inactivity
> handling. Additionally, the auto-sleep mode will be enabled. Due to the
> link bit the sensor is going to auto-sleep when inactivity was
> detected.
This to me looks like the justification that comment in the previous
patch should mention for why we enable /disable the two together.
> 
> Inactivity detection needs a threshold to be configured, and a time
> after which it will go into inactivity state if measurements under
> threshold.
> 
> When a ODR is configured this time for inactivity is adjusted with a
> corresponding reasonable default value, in order to have higher
> frequencies and lower inactivity times, and lower sample frequency but
> give more time until inactivity. Both with reasonable upper and lower
> boundaries, since many of the sensor's features (e.g. auto-sleep) will
> need to operate beween 12.5 Hz and 400 Hz. This is a default setting
> when actively changing sample frequency, explicitly setting the time
> until inactivity will overwrite the default.
> 
> Similarly, setting the g-range will provide a default value for the
> activity and inactivity thresholds. Both are implicit defaults, but
> equally can be overwritten to be explicitly configured.
> 
> Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>

A few things inline.

> @@ -307,6 +322,17 @@ static int adxl345_write_act_axis(struct adxl345_state *st,
>  					 st->act_axis_ctrl);
>  		if (ret)
>  			return ret;
> +
Probably drop this blank line.
> +	} else {
> +		st->inact_axis_ctrl = en
> +			? st->inact_axis_ctrl | ADXL345_REG_INACT_AXIS_MSK
> +			: st->inact_axis_ctrl & ~ADXL345_REG_INACT_AXIS_MSK;
> +
> +		ret = regmap_update_bits(st->regmap, ADXL345_REG_ACT_INACT_CTRL,
> +					 adxl345_act_axis_msk[type],
> +					 st->inact_axis_ctrl);
> +		if (ret)
> +			return ret;
Maybe it is worth returning in both legs of the if / else?
For this one can just return regmap_update_bits()...

>  	}
>  	return 0;
>  }
> +
> +/**
> + * adxl345_set_inact_time_s - Configure inactivity time explicitly or by ODR.
> + * @st: The sensor state instance.
> + * @val_s: A desired time value, between 0 and 255.
> + *
> + * If val_s is 0, a default inactivity time will be computed. It should take
> + * power consumption into consideration. Thus it shall be shorter for higher
> + * frequencies and longer for lower frequencies. Hence, frequencies above 255 Hz
> + * shall default to 10 s and frequencies below 10 Hz shall result in 255 s to
> + * detect inactivity.
> + *
> + * The approach simply subtracts the pre-decimal figure of the configured
> + * sample frequency from 255 s to compute inactivity time [s]. Sub-Hz are thus
> + * ignored in this estimation. The recommended ODRs for various features
> + * (activity/inactivity, sleep modes, free fall, etc.) lie between 12.5 Hz and
> + * 400 Hz, thus higher or lower frequencies will result in the boundary
> + * defaults or need to be explicitly specified via val_s.
> + *
> + * Return: 0 or error value.
> + */
> +static int adxl345_set_inact_time_s(struct adxl345_state *st, u32 val_s)
> +{
> +	unsigned int max_boundary = 255;
> +	unsigned int min_boundary = 10;
> +	unsigned int val = min(val_s, max_boundary);
> +	enum adxl345_odr odr;
> +	unsigned int regval;
> +	int ret;
> +
> +	if (val == 0) {
> +		ret = regmap_read(st->regmap, ADXL345_REG_BW_RATE, &regval);
> +		if (ret)
> +			return ret;
> +		odr = FIELD_GET(ADXL345_BW_RATE_MSK, regval);
> +
> +		val = (adxl345_odr_tbl[odr][0] > max_boundary)
> +			? min_boundary : max_boundary -	adxl345_odr_tbl[odr][0];
> +	}
> +
> +	ret = regmap_write(st->regmap, ADXL345_REG_TIME_INACT, val);
> +	if (ret)
> +		return ret;

	return regmap_write()

> +
> +	return 0;
>  }