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

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Message-ID: <554A4C6B.10703@kernel.org>
Date:	Wed, 06 May 2015 18:16:27 +0100
From:	Jonathan Cameron <jic23@...nel.org>
To:	Daniel Baluta <daniel.baluta@...el.com>,
	Lars-Peter Clausen <lars@...afoo.de>
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 06/05/15 17:25, Daniel Baluta wrote:
> 
> 
> On 05/05/2015 04:51 PM, Jonathan Cameron wrote:
>>
>>
>> On 4 May 2015 20:54:08 GMT+01:00, Lars-Peter Clausen <lars@...afoo.de> 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.
I'm confused now.  Why not?  Each hrtimer trigger created in configfs should have
it's own sampling frequency should it not? 
> 
>>>
>>> [...]
>>>> +#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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