linux-kernel - Re: [PATCH RFC 1/3] iio: Add symlink to triggers in the device's trigger folder

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Date:	Tue, 12 May 2015 20:06:52 +0100
From:	Jonathan Cameron <jic23@...nel.org>
To:	Lars-Peter Clausen <lars@...afoo.de>,
	Robert Dolca <robert.dolca@...el.com>,
	linux-iio@...r.kernel.org
CC:	linux-kernel@...r.kernel.org, Hartmut Knaack <knaack.h@....de>,
	Peter Meerwald <pmeerw@...erw.net>,
	Denis CIOCCA <denis.ciocca@...com>
Subject: Re: [PATCH RFC 1/3] iio: Add symlink to triggers in the device's
 trigger folder

On 12/05/15 17:56, Lars-Peter Clausen wrote:
> On 05/08/2015 05:11 PM, Jonathan Cameron wrote:
>> On 16/04/15 05:01, Robert Dolca wrote:
>>> This patch adds a new function called iio_trigger_register_with_dev
>>> which is a wrapper for iio_trigger_register. Besides the iio_trigger
>>> struct this function requires iio_dev struct. It adds the trigger in
>>> the device's trigger list and saves a reference to the device in the
>>> trigger's struct.
>>>
>>> When the device is registered, in the trigger folder of the device
>>> (where current_trigger file resides) a symlink is being created for
>>> each trigger that was registered width iio_trigger_register_with_dev.
>>>
>>>   # ls -l /sys/bus/iio/devices/iio:device0/trigger/
>>> total 0
>>> -rw-r--r--    1 root     root          4096 Apr 16 08:33 current_trigger
>>> lrwxrwxrwx    1 root     root             0 Apr 16 08:33 trigger0 -> ../../trigg
>>> er0
>>>
>>> This should be used for device specific triggers. Doing this the user space
>>> applications can figure out what if the trigger registered by a specific device
>>> and what should they write in the current_trigger file. Currently some
>>> applications rely on the trigger name and this does not always work.
>>>
>>> This implementation assumes that the trigger is registered before the device is
>>> registered. If the order is not this the symlink will not be created but
>>> everything else will work as before.
>>>
>>> Signed-off-by: Robert Dolca <robert.dolca@...el.com>
>> I was rather hoping we'd get a few more comments on this.
>> In principle I like the idea, but it's new ABI and does make life
>> a tiny bit more complex, so what do people think?
>>
>> Few trivial code comments inline.
> 
> I don't think it adds more information. Both the trigger and the
> device get registered for the same parent device, so you can already
> easily find the trigger for a device by going to the parent device
> and taking a look at the triggers registered by the parent device.
I had the same thought. The question is whether the slightly gain in
simplicity for userspace is worth it...  I'm undecided at the moment.
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