Re: [PATCH v4 1/3] iio: adc: Fix incorrect reading when datarate changed in single mode

[David Lechner <dlechner@baylibre.com>]

On 6/29/26 1:33 PM, Jonathan Cameron wrote:
> On Sat, 27 Jun 2026 17:31:24 -0500
> David Lechner <dlechner@baylibre.com> wrote:
> 
>> On 6/22/26 5:15 PM, Jakub Szczudlo 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 | 74 ++++++++++++++++++++++++++++++++++--
>>>  1 file changed, 70 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/iio/adc/ti-ads1100.c b/drivers/iio/adc/ti-ads1100.c
>>> index 9fe8d54cce83..e3c801381434 100644
>>> --- a/drivers/iio/adc/ti-ads1100.c
>>> +++ b/drivers/iio/adc/ti-ads1100.c
>>> @@ -15,6 +15,7 @@
>>>  #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>
>>> @@ -43,6 +44,9 @@
>>>  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 (7.5s) */
>>> +#define ADS1100_MAX_DRDY_TIMEOUT_US	7500000
>>> +
>>>  struct ads1100_data {
>>>  	struct i2c_client *client;
>>>  	struct regulator *reg_vdd;
>>> @@ -123,10 +127,49 @@ 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)
>>> +{
>>> +	int ret;
>>> +	u8 buffer[3];
>>> +
>>> +	ret = i2c_master_recv(data->client, (char *)&buffer, sizeof(buffer));  
>>
>> Do we actually need the cast here? char * is like void * and should not need it.
> Hi David,
> 
> Any more background on this?  The void * implicit cast thing is in the
> c standard.  I don't think there is anything equivalent for char *
> 
> Thanks,
> 
> Jonathan

Oops, I must have been mixing that up with special type punning
rules for char.

According to [1], char is not compatible with either of signed char
or unsigned char.

[1]: https://en.cppreference.com/c/language/type#Compatible_types