Re: [PATCH v6 1/3] iio: adc: Fix incorrect reading when datarate changed in single mode

[Jonathan Cameron <jic23@kernel.org>]

On Sat, 11 Jul 2026 20:44:12 +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.
> 
> Fixes: 541880542f2b ("iio: adc: Add TI ADS1100 and ADS1000")
> Signed-off-by: Jakub Szczudlo <jakubszczudlo40@gmail.com>
> ---
>  drivers/iio/adc/ti-ads1100.c | 67 +++++++++++++++++++++++++++++++++---
>  1 file changed, 63 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iio/adc/ti-ads1100.c b/drivers/iio/adc/ti-ads1100.c
> index 9fe8d54cce83..6ad80d42d390 100644
> --- a/drivers/iio/adc/ti-ads1100.c
> +++ b/drivers/iio/adc/ti-ads1100.c
> @@ -15,10 +15,12 @@
>  #include <linux/module.h>
>  #include <linux/init.h>
>  #include <linux/i2c.h>
> +#include <linux/iopoll.h>
>  #include <linux/mutex.h>
>  #include <linux/property.h>
>  #include <linux/pm_runtime.h>
>  #include <linux/regulator/consumer.h>
> +#include <linux/time.h>
>  #include <linux/units.h>
>  
>  #include <linux/iio/iio.h>
> @@ -43,6 +45,9 @@
>  static const int ads1100_data_rate[] = { 128, 32, 16, 8 };
>  static const int ads1100_data_rate_bits[] = { 12, 14, 15, 16 };
>  
> +/* Timeout based on the minimum sample rate of 8 SPS (7500ms) */
> +#define ADS1100_MAX_DRDY_TIMEOUT_US	(7500 * USEC_PER_MSEC)
> +
>  struct ads1100_data {
>  	struct i2c_client *client;
>  	struct regulator *reg_vdd;
> @@ -123,10 +128,46 @@ static int ads1100_get_adc_result(struct ads1100_data *data, int chan, int *val)
>  	return 0;
>  }
>  
> +static bool ads1100_new_data_not_ready(struct ads1100_data *data)
> +{
> +	u8 buffer[3];
> +	int ret;
> +
> +	ret = i2c_master_recv(data->client, (char *)&buffer, sizeof(buffer));

In theory this can return short (generally reflects a misbehaving device).

> +	if (ret < 0) {
> +		dev_err(&data->client->dev, "I2C read fail: %d\n", ret);
> +		return true;
> +	}

	if (ret < sizeof(buffer))
		return -EIO;

> +
> +	return FIELD_GET(ADS1100_CFG_ST_BSY, buffer[2]);
> +}
> +
> +static int ads1100_poll_data_ready(struct ads1100_data *data)
> +{
> +	int data_rate_Hz = ads1100_data_rate[FIELD_GET(ADS1100_DR_MASK, data->config)];
> +	/* To be sure we wait 5 times more than data rate */
> +	unsigned long wait_time_us = DIV_ROUND_CLOSEST(USEC_PER_SEC, 5 * data_rate_Hz);
> +	bool data_ready;
> +	u8 buffer[3];
> +	int ret;
> +
> +	/* To be sure that polled value will have value after config change */
> +	ret = i2c_master_recv(data->client, (char *)&buffer, sizeof(buffer));
> +	if (ret < 0) {
> +		dev_err(&data->client->dev, "I2C read fail: %d\n", ret);
> +		return ret;
> +	}
	if (ret < sizeof(buffer))
		reutrn -EIO;
> +
> +	return readx_poll_timeout(ads1100_new_data_not_ready, data,
> +				 data_ready, data_ready != 0,

Kind of related to David's question: sashiko doesn't like this.
https://sashiko.dev/#/patchset/20260711184414.1013686-1-jakubszczudlo40%40gmail.com
I think I agree with it.  Generally need to check for errors in the polling
routing as well and return those if seen (in data_ready I think at the end?)

> +				 wait_time_us, ADS1100_MAX_DRDY_TIMEOUT_US);
> +}