Re: Vibrations in input vs. LED was Re: [PATCH v2 0/3] led: ledtrig-transient: add support for hrtimer

From: Pavel Machek
Date: Sun Sep 17 2017 - 14:23:03 EST


> > If your objection is that FF is not easily engaged from the shell -
> > yes, but I do not think that actual users who want to do vibration do
> > that via shell either. On the other hand, can you drop privileges and
> > still allow a certain process control your vibrator via LED interface?
> > With FF you can pass an FD to whoever you deem worthy and later revoke
> > access.
> >
> > IOW sysfs interfaces are nice for quick hacks, but when you want to
> > use them in real frameworks, where you need to think about proper
> > namespaces, isolation, etc, etc, other kinds of interfaces might suit
> > better.
> I'd leave the decision to the user. We could add a note to the
> Documentation/leds/ledtrig-transient.txt that force feedback interface
> should be preferable choice for driving vibrate devices.

We don't want to leave decision to the user; because then we'll end up
with userland applications having to support _both_ interfaces.

Plus, it is not really your decision. Dmitry is maintainer of input
subsystem, input was doing force feedback for 10+ years, and he
already made a decision.

> However only if following conditions are met:
> - force feedback driver supports gpio driven devices
> - there is sample application in tools/input showing how to
> setup gpio driven vibrate device with use of ff interface
> - it will be possible to setup vibrate interval with 1ms accuracy,
> similarly to what the discussed patch allows to do

I agree these would be nice. Interested parties are welcome to help
there. But I don't think this should have any impact on LED
susbystem. Force feedback just does not belong to LED subsystem.

Best regards,
(cesky, pictures)

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