Re: [PATCH v2] iio: hrtimer: Allow sub Hz granularity

[Jonathan Cameron <jic23@kernel.org>]

On Sun, 13 Dec 2020 17:02:28 +0000
Jonathan Cameron <jic23@kernel.org> wrote:

> On Wed,  9 Dec 2020 14:46:44 -0800
> Gwendal Grignou <gwendal@chromium.org> wrote:
> 
> > Allow setting frequency below 1Hz or sub 1Hz precision.
> > Useful for slow sensors like ALS.
> > 
> > Test frequency is set properly:
> > modprobe iio-trig-hrtimer && \
> > mkdir /sys/kernel/config/iio/triggers/hrtimer/t1 && \
> > cd /sys/bus/iio/devices/triggerX ;
> > for i in 1 .1 .01 .001 ; do
> >   echo $i > sampling_frequency
> >   cat sampling_frequency
> > done
> > 
> > Signed-off-by: Gwendal Grignou <gwendal@chromium.org>  
> Just to note as Andy raised the ABI docs question. 
> The attribute this is providing is more generic than just for the hrtimer
> trigger and as such is in the main ABI docs.  The reason is that
> samping_frequency is able to occur in various different places depending
> on where it has side effects.  In particular a dataready trigger for
> a device with variable sampling frequency will usually be in the
> iio:\deviceX directory because it will have affects on anti aliasing filters
> so has an impact even if you are just reading from sysfs.
> We could add specific docs for this case (though because all ABI docs
> for a given named attribute need to be in one file, it would be rather
> messy).
> 
> Applied to the togreg branch of iio.git and pushed out as testing
> for the autobuilders to see if we missed anything.
> 
> Thanks,
> 
> Jonathan
> 
> 
> > ---
> > Changes since v1:
> > - Added documentation.
> > 
> >  Documentation/iio/iio_configfs.rst     |  1 +
> >  drivers/iio/trigger/iio-trig-hrtimer.c | 25 +++++++++++++++----------
> >  2 files changed, 16 insertions(+), 10 deletions(-)
> > 
> > diff --git a/Documentation/iio/iio_configfs.rst b/Documentation/iio/iio_configfs.rst
> > index ecbfdb3afef7e..428419f8732c4 100644
> > --- a/Documentation/iio/iio_configfs.rst
> > +++ b/Documentation/iio/iio_configfs.rst
> > @@ -99,3 +99,4 @@ Each trigger can have one or more attributes specific to the trigger type.
> >  
> >  "hrtimer" trigger type doesn't have any configurable attribute from /config dir.
> >  It does introduce the sampling_frequency attribute to trigger directory.
> > +That attribute sets the polling frequency in Hz, with mHz precision.
> > diff --git a/drivers/iio/trigger/iio-trig-hrtimer.c b/drivers/iio/trigger/iio-trig-hrtimer.c
> > index a5e670726717f..06acd6dc79a8c 100644
> > --- a/drivers/iio/trigger/iio-trig-hrtimer.c
> > +++ b/drivers/iio/trigger/iio-trig-hrtimer.c
> > @@ -22,7 +22,7 @@
> >  struct iio_hrtimer_info {
> >  	struct iio_sw_trigger swt;
> >  	struct hrtimer timer;
> > -	unsigned long sampling_frequency;
> > +	int sampling_frequency[2];
> >  	ktime_t period;
> >  };
> >  
> > @@ -38,7 +38,9 @@ ssize_t iio_hrtimer_show_sampling_frequency(struct device *dev,
> >  	struct iio_trigger *trig = to_iio_trigger(dev);
> >  	struct iio_hrtimer_info *info = iio_trigger_get_drvdata(trig);
> >  
> > -	return snprintf(buf, PAGE_SIZE, "%lu\n", info->sampling_frequency);
> > +	return iio_format_value(buf, IIO_VAL_INT_PLUS_MICRO,
> > +			ARRAY_SIZE(info->sampling_frequency),
> > +			info->sampling_frequency);
> >  }
> >  
> >  static
> > @@ -48,18 +50,21 @@ ssize_t iio_hrtimer_store_sampling_frequency(struct device *dev,
> >  {
> >  	struct iio_trigger *trig = to_iio_trigger(dev);
> >  	struct iio_hrtimer_info *info = iio_trigger_get_drvdata(trig);
> > -	unsigned long val;
> > -	int ret;
> > +	unsigned long long val;
> > +	int integer, fract, ret;
> >  
> > -	ret = kstrtoul(buf, 10, &val);
> > +	ret = iio_str_to_fixpoint(buf, 100, &integer, &fract);
> >  	if (ret)
> >  		return ret;
> >  
> > -	if (!val || val > NSEC_PER_SEC)
> > +	val = fract + 1000 * integer;
> > +
> > +	if (!val || val > NSEC_PER_SEC * 1000)
> >  		return -EINVAL;
> >  
> > -	info->sampling_frequency = val;
> > -	info->period = NSEC_PER_SEC / val;
> > +	info->sampling_frequency[0] = integer;
> > +	info->sampling_frequency[1] = fract * 1000;
> > +	info->period = NSEC_PER_SEC * 1000 / val;

0 day pointed out this is a 64 bit division so needs to work on 32 bit platforms.

I've dropped it for now, please respin with that fixed up.

Thanks,

Jonathan

> >  
> >  	return len;
> >  }
> > @@ -135,8 +140,8 @@ static struct iio_sw_trigger *iio_trig_hrtimer_probe(const char *name)
> >  	hrtimer_init(&trig_info->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> >  	trig_info->timer.function = iio_hrtimer_trig_handler;
> >  
> > -	trig_info->sampling_frequency = HRTIMER_DEFAULT_SAMPLING_FREQUENCY;
> > -	trig_info->period = NSEC_PER_SEC / trig_info->sampling_frequency;
> > +	trig_info->sampling_frequency[0] = HRTIMER_DEFAULT_SAMPLING_FREQUENCY;
> > +	trig_info->period = NSEC_PER_SEC / trig_info->sampling_frequency[0];
> >  
> >  	ret = iio_trigger_register(trig_info->swt.trigger);
> >  	if (ret)  
>