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

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Date:	Mon, 04 May 2015 21:54:08 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Daniel Baluta <daniel.baluta@...el.com>, jic23@...nel.org
CC:	jlbec@...lplan.org, knaack.h@....de, linux-kernel@...r.kernel.org,
	linux-iio@...r.kernel.org, octavian.purdila@...el.com,
	pebolle@...cali.nl, patrick.porlan@...el.com,
	adriana.reus@...el.com, constantin.musca@...el.com,
	marten@...uitiveaerial.com
Subject: Re: [PATCH v5 3/4] iio: trigger: Introduce IIO hrtimer based trigger

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.

[...]
> +#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.
[...]
> +}
> +
> +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.

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

const

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

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