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

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Message-ID: <20170917182251.GA15328@amd>
Date:   Sun, 17 Sep 2017 20:22:51 +0200
From:   Pavel Machek <pavel@....cz>
To:     Jacek Anaszewski <jacek.anaszewski@...il.com>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
        David Lin <dtwlin@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Richard Purdie <rpurdie@...ys.net>,
        Hans de Goede <hdegoede@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh@...nel.org>,
        Rom Lemarchand <romlem@...gle.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>
Subject: Re: Vibrations in input vs. LED was Re: [PATCH v2 0/3] led:
 ledtrig-transient: add support for hrtimer

Hi!

> > 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,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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