On Wed, May 13, 2015 at 8:42 PM, Jonathan Cameron <jic23@xxxxxxxxxx> wrote: > > On 13/05/15 08:28, Lars-Peter Clausen wrote: > > On 05/12/2015 09:06 PM, Jonathan Cameron wrote: > >> 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@xxxxxxxxx> > >>>> 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. > > > > As you may have guessed by now I'm always quite conservative when it > > comes to introducing new ABI. Simply because we have to maintain it > > forever, the less stuff to maintain forever the better. > > > > Hence I think all new ABI needs a compelling reason, e.g. like a > > improvement in performance. And of course this patch slightly > > simplifies things, but in my opinion not enough to justify a ABI > > extension. We can always find ways to simplify the interface, but the > > metric for ABI should be whether the simplification actually matters. > > In this case I don't think it does, finding the trigger for a device > > is not really hot-path. The amount of time saved will be disappear in > > the noise. > > > > And in my opinion applications shouldn't directly use the low-level > > ABI but rather use middle-ware libraries/frameworks, like e.g. > > libiio, and that's where you'd hide the complexities of a operation. > > > > - Lars > I'll go with Lars response on this one. Not worth the hassle. > That's the nature of an RFC of course! > > Jonathan Would it be acceptable to add the symlinks without adding a new API? When a trigger is registered you could use the common parent to get a pointer to the iio_dev and then create the symlink. This is a little bit complicated but I think it can be done. Robert -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
