Re: [PATCH] iio: imu: st_lsm6dsx: do not roundup set samplerate

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> On 10/05/2021 14.07, Lorenzo Bianconi wrote:
> >> On 10/05/2021 08.28, Lorenzo Bianconi wrote:
> >>>> On 07/05/2021 13.02, Lorenzo Bianconi wrote:
> >>>>>> The correct way to set the sampling rate to 12.5 Hz before
> >>>>>> commit f8710f0357bc ("iio: imu: st_lsm6dsx: express odr in mHZ")
> >>>>>> was to write 13 Hz to sampling_frequency.
> >>>>>> Before this patch writing 13 to samplerate results in sample rate set
> >>>>>> to 26 Hz.
> >>>>>> Now we return EINVAL if the sampling rate is not in table.
> >>>>>>
> >>>>>> Signed-off-by: Sean Nyekjaer <sean@geanix.com>
> >>>>>
> >>>>> I think this patch is breaking i2c-master support available in st_lsm6dsx, have you tested it?
> >>>>>
> >>>> I have not tested with i2c-master.
> >>>> But it's not nice to round up sample rate from user space without any notice.
> >>>
> >>> the point is accel odr is used as trigger for i2c-slave sampling. Connected
> >>> i2c slave devices have different sample rates (e.g. LIS2MDL), so we need to
> >>> select the lower accel odr greather than slave device one.
> >>>
> >>> Regards,
> >>> Lorenzo
> >>>
> >>
> >> We could open up for custom sample rates if i2c-slaves are enabled?
> > 
> > can you please explain what you mean?
> > 
> If i2c-slaves are enabled, it's allowed to set off table sample rates.(We roundup samplerate like now)
> If i2c-slaves are disabled, we return -EINVAL if we can't find the chosen samplerate in the samplerate table?

IMO this is not a big deal because if you set the proper ODR (e.g. 26Hz) with the
i2c-master disabled, the sample rate will not be rounded-up. If you set 20Hz,
the accel ODR will be set to 26Hz. I think it does not worth to make the code
uglier and more complex to maintain.

Regards,
Lorenzo

> 
> /Sean

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