linux-kernel - Re: [PATCH v4 01/24] input: Add ff-memless-next module

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Message-ID: <CADbOyBTjC-Gfx+gKo0VRbnKMLFvNpQzo9a-VHRPMUuTNLGoiqw@mail.gmail.com>
Date:	Thu, 22 May 2014 11:48:11 +0200
From:	Elias Vanderstuyft <elias.vds@...il.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Simon Wood <simon@...gewell.org>,
	"open list:HID CORE LAYER" <linux-input@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Anssi Hannula <anssi.hannula@....fi>,
	Michal Malý <madcatxster@...oid-pointer.net>,
	Roland Bosa <rbosa@...itech.com>
Subject: Re: [PATCH v4 01/24] input: Add ff-memless-next module

On Tue, May 20, 2014 at 11:26 PM, Elias Vanderstuyft
<elias.vds@...il.com> wrote:
> On Tue, May 20, 2014 at 10:58 PM, Michal Malý
> <madcatxster@...oid-pointer.net> wrote:
>> On Tuesday 20 of May 2014 16:16:12 simon@...gewell.org wrote:
>>> Regarding the question of emulated vs. real effects, can we extend the API
>>> so that applications can know which effects are really supported, and
>>> enable/disable emulation somehow?
>>
>> I suppose that a few extra flags (FF_PERIODIC_EMULATED etc.) defined in
>> "uapi/linux/input.h" should suffice.
>
> @Dmitry:
> Now that we're talking about API changes, I would like to propose some
> additional things in the Linux FF API:
>
> - Possibility to *get* FF state variables, such as the value of the
> current GAIN, and the current AUTOCENTER:
> At the moment, only *setting* is possible.
> This poses a problem when implementing proper AUTOCENTER state
> recovery (upon closing a Windows program) in Wine, because the initial
> AUTOCENTER state was unknown.
> The same applies for GAIN.
>
> - Introduce multiple types of GAIN, apart from the current global
> GAIN, e.g. GAIN_CONSTANT and GAIN_DAMPER:
> This is mainly on request of some users, especially Logitech users: on
> Windows Logitech additionally supports to set the global Damper and
> Spring gain.
> Maybe it would be nicer to create a global gain for every supported
> Linux FF effect?

And Roland Bosa (from Logitech) also agrees with the following
addition/modification to the Linux FF API:

- Infinite iterations, or in Linux FF terms: playback of an effect
with an event count of infinity.
Right now, an event count of zero stops the effect, while the maximum
count is INT_MAX.
An event count value of '-1' can be used to indicate infinity.
(However note that it is somewhat inconsistent with the infinite
effect "duration" we already support: in that case '0' is used)
Is this feasible? (in terms of backward compatibility)

Thanks,
Elias
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