linux-kernel - Re: FF layer restrictions [Was: [PATCH 1/1] Input: add sensable phantom driver]

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Date:	Wed, 21 Mar 2007 21:04:08 +0100
From:	Jiri Slaby <jirislaby@...il.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
CC:	johann deneux <johann.deneux@...il.com>,
	"STenyaK (Bruno González)" 
	<stenyak@...il.com>, Anssi Hannula <anssi.hannula@...il.com>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	linux-input@...ey.karlin.mff.cuni.cz
Subject: Re: FF layer restrictions [Was: [PATCH 1/1] Input: add sensable phantom
 driver]

Dmitry Torokhov napsal(a):
> On 3/21/07, johann deneux <johann.deneux@...il.com> wrote:
>> I would suggest adding a new effect type (3d effect) and extending the
>> union in struct ff_effect.
>> Let me know if I'm too vague, I already suggested that solution but
>> got no answer. I wonder if my mail got lost, nobody understood what I
>> said, or if it's just a plain bad idea.
>>
> 
> My concern with a new 3D effect is that it will be a very "simple"
> effect with only constant force apllied. That might be enough for
> phantom but may not be sufficient for future devices. If we add
> ability to specify a "plane" for an effect we will be able to add
> envelopes on top of more complex effects and get desired combined
> effcet.

I didn't get this too much, because I don't understand the FF layer well so
far. How is this going to work? Let's say, we have 3 torque values computed
in US, and this structure:

struct ff_effect {
    __u16 direction;
    struct ff_trigger trigger;
    struct ff_replay replay;

    struct ff_constant_effect {
        __s16 level;
 	struct ff_envelope {
   	     __u16 attack_length;
    	     __u16 attack_level;
   	     __u16 fade_length;
     	     __u16 fade_level;
	};
    };
};

and need to pass the three 16bits torques into s16 ioaddr[0..2]. How?

> I would not worry aboput extra memory needed on I-force like
> devices because they just would not support additional "planes". What
> about phantom? Would it have enough memory?

It's a memless device -- values written into pci space are immediately felt
in FF (it's just PLX chip interface to some their proprietary chip or somewhat).

> On the other hand if you guys (Anssi, Johann, Jiri...) decide that a
> simple new 3d effect is the most efficient solution for now and will
> be enough for a few years (till we get FF v2 API) I will merge it.

I won't force any of mentioned solutions, but this seems the simplest one in
my eyes.

thanks for clues,
-- 
http://www.fi.muni.cz/~xslaby/            Jiri Slaby
faculty of informatics, masaryk university, brno, cz
e-mail: jirislaby gmail com, gpg pubkey fingerprint:
B674 9967 0407 CE62 ACC8  22A0 32CC 55C3 39D4 7A7E
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