Re: [PATCH v3 3/3] iio: adc: Fix incorrect reading when datarate changed in single mode

[Jonathan Cameron <jic23@kernel.org>]

On Sat, 13 Jun 2026 21:09:57 +0200
Jakub Szczudlo <jakubszczudlo40@gmail.com> wrote:

> When device is suspended and it is in single mode then changing
> datarate doesn't make it actual wait for new measurement, so to
> be sure that read after change is correct functions that changes
> datarate and gain will wait for new data.

Fix should normally be the first patch in the series to make it
easier (or at least more obvious) to backport.

Also needs a fixes tag.

A few things inline,

thanks,

Jonathan

> 
> Signed-off-by: Jakub Szczudlo <jakubszczudlo40@gmail.com>
> ---
>  drivers/iio/adc/ti-ads1100.c | 55 ++++++++++++++++++++++++++++++++++--
>  1 file changed, 52 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/adc/ti-ads1100.c b/drivers/iio/adc/ti-ads1100.c
> index 76de2466dc53..195394665cd1 100644
> --- a/drivers/iio/adc/ti-ads1100.c
> +++ b/drivers/iio/adc/ti-ads1100.c
> @@ -123,6 +123,36 @@ static int ads1100_get_voltage_microvolts(struct ads1100_data *data)
>  	return ads1100_get_voltage_milivolts(data) * MICRO / MILLI;
>  }
>  
> +static bool ads1100_new_data_ready(struct ads1100_data *data)
> +{
> +	int ret;
> +	u8 buffer[3];
> +
> +	ret = i2c_master_recv(data->client, (char *)&buffer, sizeof(buffer));
> +	if (ret < 3) {
> +		dev_err(&data->client->dev, "I2C read fail: %d\n", ret);
> +		return ret;

This is odd given it returns bool (and don't print ret = 1 or 2 here as that
is rather unexpected in an error print.).


> +	}
> +
> +	return FIELD_GET(ADS1100_CFG_ST_BSY, buffer[2]);
> +}
> +
> +static int ads1100_poll_data_ready(struct ads1100_data *data)
> +{
> +	u8 buffer[3];
> +	bool data_ready;
> +	int datarate = data->ads_config->data_rate[FIELD_GET(ADS1100_DR_MASK, data->config)];
> +   // To be sure we wait 5 times more than datarate

Left over from writing the code?  If you want a comment then /* */ and
get the indent right.

> +	unsigned long wait_time = DIV_ROUND_CLOSEST(MICRO, 5 * datarate);
> +
> +	/* To be sure that polled value will have value after config change */
> +	i2c_master_recv(data->client, (char *)&buffer, sizeof(buffer));

Check return value probably even though we don't care about the data.

> +
> +	return read_poll_timeout(ads1100_new_data_ready, data_ready,
> +				 !data_ready, wait_time,
> +				 ADS1100_MAX_DRDY_TIMEOUT, false, data);
> +}
> +
>  static int ads1100_data_bits(struct ads1100_data *data)
>  {
>  	return ads1100_data_rate_bits[FIELD_GET(ADS1100_DR_MASK, data->config)];
> @@ -165,6 +194,7 @@ static int ads1100_set_scale(struct ads1100_data *data, int val, int val2)
>  {
>  	int microvolts;
>  	int gain;
> +	int ret;
>  
>  	/* With Vdd between 2.7 and 5V, the scale is always below 1 */
>  	if (val)
> @@ -185,21 +215,40 @@ static int ads1100_set_scale(struct ads1100_data *data, int val, int val2)
>  	if (gain < BIT(0) || gain > BIT(3))
>  		return -EINVAL;
>  
> +	ret = pm_runtime_resume_and_get(&data->client->dev);
> +	if (ret < 0)
> +		return ret;

Might be worth looking at the ACQUIRE macros in pm_runtime.h as they might simpify things
a little.

> +
>  	ads1100_set_config_bits(data, ADS1100_PGA_MASK, ffs(gain) - 1);
>  
> -	return 0;
> +	ret = ads1100_poll_data_ready(data);
> +
> +	pm_runtime_put_autosuspend(&data->client->dev);
> +
> +	return ret;
>  }
>  
>  static int ads1100_set_data_rate(struct ads1100_data *data, int chan, int rate)
>  {
>  	unsigned int i;
>  	unsigned int size;
> +	int ret;
>  
>  	size = data->supports_data_rate ? ARRAY_SIZE(ads1100_data_rate) : 1;
>  	for (i = 0; i < size; i++) {
> -		if (data->ads_config->data_rate[i] == rate)
> -			return ads1100_set_config_bits(data, ADS1100_DR_MASK,
> +		if (data->ads_config->data_rate[i] != rate)
> +			continue;
> +
> +		ret = pm_runtime_resume_and_get(&data->client->dev);
> +		if (ret < 0)
> +			return ret;
> +
> +		ads1100_set_config_bits(data, ADS1100_DR_MASK,
>  					FIELD_PREP(ADS1100_DR_MASK, i));
> +		ret = ads1100_poll_data_ready(data);
> +
> +		pm_runtime_put_autosuspend(&data->client->dev);
> +		return ret;
>  	}
>  
>  	return -EINVAL;