Re: IIO timestamp get skewed when suspending (st_lsm6dsx)

[Sean Nyekjaer <sean@geanix.com>]

On 03/06/2020 10.06, Lorenzo Bianconi wrote:
>>
>>
>> On 02/06/2020 15.39, Sean Nyekjaer wrote:
>>>>> are these values from the hw FIFO? can you please add
>>>>> sensor->ts_ref to the trace and
>>>>> a log into st_lsm6dsx_reset_hw_ts?
>>>>>
>>>>
>>>> Hi,
>>>>
>>>> This certainly looks weird,
>>>>
>>>> https://gist.github.com/sknsean/b32bae140008cf446a8fea58e305da47
>>>>
>>>> Seems like the ts_ref is updated and used but not read/used in
>>>> userspace...
>>>>
>>>> /Sean
>>>
>>> added to st_lsm6dsx_read_fifo :
>>>
>>> printk("ts_ref %lld, ts %lld, sample_time %lld\n", acc_sensor->ts_ref,
>>> ts, acc_sensor->ts_ref + ts);
>>>
>>> https://gist.github.com/sknsean/3ad1e9e05cb0e2ef811a3c83492a1980
>>>
>>> Suspend again was 15sec
>>>
>>> /Sean
>>
>> Hi,
>>
>> Some more findings :)
>> https://gist.github.com/sknsean/d31e48b65515361309cd238dcf68600f
>>
>> To me it looks like ktime_get_real_ns() isn't ready or updated when we are
>> calling iio_get_time_ns().
>> If we look in the trace ktime_get_real_ns() it's ready when we are getting
>> the first sample after suspend.
>>
>> Running with this patch:
>> https://gist.github.com/sknsean/415d1b9c34f20db4419a0c61a58eb188
>> +
>> The first from this thread.
>>
>> /Sean
> 
> Hi Sean,
> 
> looking at the logs I guess we should not reset the sensor hw ts. Could you
> please try the below patch?
> 
> Regards,
> Lorenzo
> 
> diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> index 0b776cb91928..4f8a9bcee77b 100644
> --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> @@ -2445,6 +2445,8 @@ static int __maybe_unused st_lsm6dsx_resume(struct device *dev)
>   		if (!(hw->suspend_mask & BIT(sensor->id)))
>   			continue;
>   
> +		sensor->ts_ref = iio_get_time_ns(hw->iio_devs[i]);
> +
>   		if (sensor->id == ST_LSM6DSX_ID_EXT0 ||
>   		    sensor->id == ST_LSM6DSX_ID_EXT1 ||
>   		    sensor->id == ST_LSM6DSX_ID_EXT2)
> 

Hmm, suspend again for 15s.

https://gist.github.com/sknsean/911ae4ae2e74ebe1e7eca1405c645ff1

[  105.520634] PM: suspend exit
[  105.540206] ts_ref 1591097307780181385, ts 2861700000, sample_time 
1591097310641881385

[  105.548416] ktime_get_real_ns: 1591097322928175385

CLOCK_REALTIME isn't ready in the resume function. I think we need to 
link it to CLOCK_BOOTTIME (Which ticking under suspend) instead.

/Sean