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Message-ID: <27b1b6cf-759c-4778-a53c-5d01442120b7@redhat.com>
Date: Tue, 16 Apr 2024 10:33:00 +0200
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Subject: Re: [PATCH 1/4] Input: Add trackpoint doubletap and system debug info
 keycodes
To: Mark Pearson <mpearson-lenovo@squebb.ca>,
 Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Peter Hutterer <peter.hutterer@redhat.com>,
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 linux-input@vger.kernel.org, linux-kernel@vger.kernel.org,
 Nitin Joshi1 <njoshi1@lenovo.com>, Vishnu Sankar <vsankar@lenovo.com>
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From: Hans de Goede <hdegoede@redhat.com>
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Hi Mark,

On 4/16/24 1:57 AM, Mark Pearson wrote:
> Hi Dmitry,
> 
> On Mon, Apr 15, 2024, at 6:54 PM, Dmitry Torokhov wrote:
>> On Mon, Apr 15, 2024 at 04:28:19PM -0400, Mark Pearson wrote:
>>> Hi
>>>
>>> On Mon, Apr 15, 2024, at 3:58 PM, Dmitry Torokhov wrote:
>>>> On Mon, Apr 15, 2024 at 09:50:37PM +0200, Hans de Goede wrote:
>>>>> Hi,
>>>>>
>>>>> On 4/15/24 9:40 PM, Dmitry Torokhov wrote:
>>>>>> On Wed, Apr 10, 2024 at 10:48:10PM -0400, Mark Pearson wrote:
>>>>>>>
>>>>>>> I have a stronger preference to keep the KEY_DOUBLECLICK - that one seems less controversial as a genuine new input event.
>>>>>>
>>>>>> Please see my response to Peter's letter. I think it very much depends
>>>>>> on how it will be used (associated with the pointer or standalone as it
>>>>>> is now).
>>>>>>
>>>>>> For standalone application, recalling your statement that on Win you
>>>>>> have this gesture invoke configuration utility I would argue for
>>>>>> KEY_CONFIG for it.
>>>>>
>>>>> KEY_CONFIG is already generated by Fn + F# on some ThinkPads to launch
>>>>> the GNOME/KDE control center/panel and I believe that at least GNOME
>>>>> comes with a default binding to map KEY_CONFIG to the control-center.
>>>>
>>>> Not KEY_CONTROLPANEL?
>>>>
>>>> Are there devices that use both Fn+# and the doubleclick? Would it be an
>>>> acceptable behavior for the users to have them behave the same?
>>>>
>>> Catching up with the thread, thanks for all the comments.
>>>
>>> For FN+N (originally KEY_DEBUG_SYS_INFO) the proposal was to now use
>>> KEY_VENDOR there. My conclusion was that this is targeting vendor
>>> specific functionality, and that was the closest fit, if a new keycode
>>> was not preferred.
>>
>> Fn+N -> KEY_VENDOR mapping sounds good to me.
>>
>>>
>>> For the doubletap (which is a unique input event - not related to the
>>> pointer) I would like to keep it as a new unique event. 
>>>
>>> I think it's most likely use would be for control panel, but I don't
>>> think it should be limited to that. I can see it being useful if users
>>> are able to reconfigure it to launch something different (browser or
>>> music player maybe?), hence it would be best if it did not conflict
>>> with an existing keycode function. I also can't confirm it doesn't
>>> clash on existing or future systems - it's possible.
>>
>> So here is the problem. Keycodes in linux input are not mere
>> placeholders for something that will be decided later how it is to be
>> used, they are supposed to communicate intent and userspace ideally does
>> not need to have any additional knowledge about where the event is
>> coming from. A keyboard either internal or external sends KEY_SCREENLOCK
>> and the system should lock the screen. It should not be aware that one
>> device was a generic USB external keyboard while another had an internal
>> sensor that recognized hovering palm making swiping motion to the right
>> because a vendor decided to make it. Otherwise you have millions of
>> input devices all generating unique codes and you need userspace to
>> decide how to interpret data coming from each device individually.
>>
>> If you truly do not have a defined use case for it you have a couple
>> options:
>>
>> - assign it KEY_RESERVED, ensure your driver allows remapping to an
>>   arbitrary keycode, let user or distro assign desired keycode to it
>>
>> - assign KEY_PROG1 .. KEY_PROG4 - pretty much the same - leave it in the
>>   hand of the user to define a shortcut in their DE to make it useful
>>
>>>
>>> FWIW - I wouldn't be surprised with some of the new gaming systems
>>> we're seeing (Steamdeck, Legion-Go, etc), that a doubletap event on a
>>> joystick might be useful to have, if the HW supports it?
>>
>> What would it do exactly? Once we have this answer we can define key or
>> button code (although I do agree that game controller buttons are
>> different from "normal" keys because they map to the geometry of the
>> controller which in turn defines their commonly understood function).
>>
>> But in any case you would not reuse the same keycode for something that
>> is supposed to invoke a configuration utility and also to let's say
>> drop a flash grenade in a game.
>>
> 
> Understood.
> 
> I don't see a path forward within your stated parameters. I did not realise that there were such limitations, so my apologies for wasting everybody's time, and thank you for your patience and guidance.
> 
> I will drop this patch from the series and proceed using existing defined codes only.
> 
> Hans, I'll need to rejig things a bits but I have some ideas and I think I can make it work and stay within the pdx86 tree, which will make it simpler.

Ok this sounds good to me. For Fn + N using KEY_VENDOR sounds good for
me and for the doubletap any one of KEY_CONFIG/KEY_CONTROLPANEL/KEY_INFO/KEY_PROG1
or some other suitable KEY_foo define works for me.

Regards,

Hans