linux-kernel - Re: Using EV_MSC or extending KEY

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Message-ID: <2c0ac825ebe78da99328b896faae04a2.squirrel@intranet.cs.nmsu.edu>
Date:	Wed, 16 Sep 2009 15:27:11 -0600
From:	"Rick L. Vinyard, Jr." <rvinyard@...nmsu.edu>
To:	"Dmitry Torokhov" <dmitry.torokhov@...il.com>
Cc:	"Trilok Soni" <soni.trilok@...il.com>,
	"Linux USB" <linux-usb@...r.kernel.org>,
	"LKML" <linux-kernel@...r.kernel.org>, linux-input@...r.kernel.org
Subject: Re: Using EV_MSC or extending KEY_*

Dmitry Torokhov wrote:
> On Tue, Sep 15, 2009 at 01:05:57PM -0600, Rick L. Vinyard, Jr. wrote:
>> Dmitry Torokhov wrote:
>> > On Tue, Sep 15, 2009 at 10:41:30PM +0530, Trilok Soni wrote:
>> >> Adding linux-input.
>> >>
>> >> On Tue, Sep 15, 2009 at 9:49 PM, Rick L. Vinyard, Jr.
>> >> <rvinyard@...nmsu.edu> wrote:
>> >> > On the Logitech G13 there are a set of 10 special keys at the top
>> of
>> >> the
>> >> > device.
>> >> >
>> >> > I've written the driver so that it maintains a map from the general
>> >> keys
>> >> > (G1-G22) to Linux' input subsystem keys.
>> >> >
>> >> > The map can be changed on the fly, allowing multiple keymaps to be
>> >> loaded.
>> >> >
>> >> > As a side note I haven't provided for this functionality (multiple
>> >> > keymaps) in the driver since this can be maintained from userspace,
>> >> but it
>> >> > does need to know about the currently loaded keymap so that when
>> the
>> >> raw
>> >> > HID events are parsed the appropriate EV_KEY events can be input.
>> >> >
>> >> > I could set it up so that the special keys also map to a KEY_*
>> code.
>> >> > However, I'd prefer to set things up so that any G1-G22 key can be
>> >> mapped
>> >> > to any input subsystem KEY_* code and not reserve a set of 10 from
>> the
>> >> > current KEY_* codes for the 10 special keys.
>> >> >
>> >> > One way I was thinking of approaching this was to generate EV_MSC
>> type
>> >> > events (with a MSC_RAW code) using the value to indicate the state
>> >> > (pressed/released) and special key.
>> >
>> > Doesn't HID already generate EV_MSC/MSC_SCAN for exactly this purpose
>> > so userspace knows what keys can be remapped? You may initially map
>> all
>> > keys you don't know the usage to KEY_UNKNOWN.
>>
>> As I understand it the EV_MSC/MSC_SCAN is used to trigger a prompting of
>> the user to map a key, which would be useful for the G1-G22 keys and
>> perhaps 5 of the 10 special keys. But, that's not the behavior I want
>> for
>> the M1, M2, M3, MR and backlight keys.
>>
>> Somehow they need to be distinct from any existing KEY_* codes or not
>> have
>> a code at all... i.e. only emitting the raw misc events.
>>
>> Perhaps the BTN_MISC codes are better suited for these keys?
>>
>
> I am sorry, I don't follow... why would yo not want to assign a standard
> code to the M* keys?
>
> --
> Dmitry

The M* keys are intended to provide a quick way to switch between key
mappings, with each mode having their own user-defined mappings.

So, if it is intended for the user to potentially program any of the G*
keys to anything within the set of existing keys (KEY_*, BTN_*) then the
M* keys need something outside that set to signal their events.

That's why I was thinking that EV_MSC/MSC_RAW could encode both the key
and the state (Pressed/Released) outside the set of existing keys.

---

Rick


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