Re: [PATCH v5 3/4] iio: trigger: Introduce IIO hrtimer based trigger

[Daniel Baluta]

On 05/05/2015 04:51 PM, Jonathan Cameron wrote:
> On 4 May 2015 20:54:08 GMT+01:00, Lars-Peter Clausen <lars@xxxxxxxxxx> wrote:
> > On 05/04/2015 12:50 PM, Daniel Baluta wrote:
> > [...]
> > > +IIO_HRTIMER_INFO_ATTR(sampling_frequency, S_IRUGO | S_IWUSR,
> > > +		      iio_hrtimer_info_show_sampling_frequency,
> > > +		      iio_hrtimer_info_store_sampling_frequency);
> >
> > I wonder if the sampling frequency should be configurable the regular
> > IIO
> > API, just like any other IIO device. But things like min/max sampling
> > frequency should be configured in configfs.
> Would have to be in the trigger dir rather than device... Makes sense to put it there.
> Limits on it here seem like a sensible idea.

But then each trigger will have sampling_frequency right? This is not 
what we want.

> > [...]
> > > +#endif /* CONFIGFS_FS */
> > > +
> > [...]
> > > +static struct iio_sw_trigger *iio_trig_hrtimer_probe(const char
> > *name)
> > > +{
> > [...]
> > > +#ifdef CONFIG_CONFIGFS_FS
> > > +	config_group_init_type_name(&trig_info->swt.group, name,
> > > +				    &iio_hrtimer_type);
> > > +#endif
> >
> > This should probably have a helper function in the sw trigger core,
> > that
> > gets stubbed out when CONFIG_FS is disabled. Otherwise we'll see the
> > same
> > #ifdef in every software trigger driver.
> > [...]

Agree with this. Will fix.

> > > +}
> > > +
> > > +static int iio_trig_hrtimer_remove(struct iio_sw_trigger *swt)
> > > +{
> > > +	struct iio_hrtimer_info *trig_info;
> > > +
> > > +	trig_info = iio_trigger_get_drvdata(swt->trigger);
> > > +
> > > +	hrtimer_cancel(&trig_info->timer);
> > > +
> > > +	iio_trigger_unregister(swt->trigger);
> > > +	iio_trigger_free(swt->trigger);
> >
> > There is a bit of a race condition here. hrtimer_cancel() should be
> > called
> > between unregister and free, otherwise it might be re-armed before it
> > is
> > unregistered.

So this can be re-armed only if the buffer is re-enabled between 
hrtimer_cancel and iio_trigger_unregister :). I'm trying to understand 
how the race can happen.


> > > +	kfree(trig_info);
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +struct iio_sw_trigger_ops iio_trig_hrtimer_ops = {
> >
> > const

Agree.
> > > +	.probe		= iio_trig_hrtimer_probe,
> > > +	.remove		= iio_trig_hrtimer_remove,
> > > +};
> > [...]
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