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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Date:   Mon, 18 Sep 2017 22:50:06 +0200
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Pavel Machek <pavel@....cz>
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,

On 09/17/2017 08:22 PM, Pavel Machek wrote:
> 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.

This state has lasted for five years now. I don't recall any
complaints. Do you?

> 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.

It seems that you applied a fait accompli method here.

Actually could you share what the decision is? AFAIK we're not
discussing here any patch for the input subsystem?

>> 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.

You cut off important piece of my text from the beginning of this
paragraph. It was:

> 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.
> However only if following conditions are met:

What I meant is that it is my decision, as a LED subsystem maintainer,
to accept the addition of a note about some other subsystem offering
an equivalent or even better substitute of the feature being available
in the subsystem I am responsible for. And I will accept such a patch
only if mentioned conditions are met.

-- 
Best regards,
Jacek Anaszewski