linux-kernel - Re: [PATCH] Add BTN_TOOL

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Message-ID: <AANLkTi=_swc-_J+hO-UWYh1sbQj=Lr2gFW-rK88fE6Z6@mail.gmail.com>
Date:	Tue, 23 Nov 2010 17:10:50 -0800
From:	Ping Cheng <pinglinux@...il.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	linux-kernel@...r.kernel.org, jkosina@...e.cz
Subject: Re: [PATCH] Add BTN_TOOL_BUTTONS to input.h

On Tue, Nov 23, 2010 at 4:51 PM, Ping Cheng <pinglinux@...il.com> wrote:
> On Tue, Nov 23, 2010 at 4:38 PM, Dmitry Torokhov
> <dmitry.torokhov@...il.com> wrote:
>> On Tue, Nov 23, 2010 at 04:12:13PM -0800, Ping Cheng wrote:
>>> On Tue, Nov 23, 2010 at 2:24 PM, Dmitry Torokhov
>>> <dmitry.torokhov@...il.com> wrote:
>>> >
>>> >> > The BTN_TOOL_* were introduced to indicate to the userspace tool that is
>>> >> > currently touching the surface of the device. Buttons are expected to be
>>> >> > always present and can change their state regardless of what tool is
>>> >> > being used at the moment. I.e. The full hardware state (between
>>> >> > EV_SYN/SYN_REPORT) could be, for example,
>>> >> >
>>> >> > Pen at 10,20, BTN_0, and BTN_2 (ABS_X 10, ABS_Y 20, BTN_TOOL_PEN, BTN_0,
>>> >> > BTN_2) or
>>> >> >
>>> >> > Lens at 20,15 and BTN_1 (ABS_X 20, ABS_Y 15, BTN_TOOL_LENS, BTN_1).
>>> >> >
>>> >> > As you can see BTN_* events can accompany either BTN_TOOL_LENS or
>>> >> > BTN_TOOL_PEN or any other BTN_TOOL_*.
>>> >>
>>> >> You are right. The tablet buttons can go with one of those other
>>> >> BTN_TOOL_s _if_ they do not define the same event types (BTN_s) as the
>>> >> tablet buttons.
>>> >>
>>> >> The new Bamboo MT code sends both BTN_LEFT and BTN_RIGHT events for
>>> >> Tablet Buttons (refer to line 905 and 908 of wacom_wac.c). However,
>>> >> BTN_LEFT and BTN_RIGHT are also sent by BTN_TOOL_MOUSE/LENS tool
>>> >> (refer to wacom_wac.c line 622 to 665).
>>> >>
>>> >> If we remove BTN_TOOL_FINGER without a BTN_TOOL-something to replace
>>> >> it, the two LEFT and RIGHT buttons will have a hard time to tell the
>>> >> user land if they are from the MOUSE/LENS or the Tablet Buttons. The
>>> >> worst case could be the LEFT/RIGHT sent later overwrites the earlier
>>> >> ones.
>>> >>
>>> >> We could do some guesswork in the user land to figure out which
>>> >> LEFT/RIGHT belongs to which BTN_TOOL_ if the above scenario does not
>>> >> happen. But, it would be much cheaper and more reliable if we can tell
>>> >> the user land where those LEFT and RIGHT come from. This is the whole
>>> >> purpose of the kernel driver, isn't it?
>>> >
>>> > What would userspace want to figure what physical button was pressed?
>>> > Input events convey _actions_, i.e. BTN_LEFT means that user pressed
>>> > primary button on the device. It does not matter if it was pressed on
>>> > tablet or the mouse/lens; the response should be the same.
>>>
>>> You're right, if the user wants a LEFT click. In a lot of cases, they
>>> want to translate it into something else. LEFT is only a default value
>>> that we give them if they do nothing.
>>>
>>> > If you expect different response, depending on which physical button is
>>> > pressed, then they should emit different BTN_* events. If you are
>>> > concerned that some users might want to have the same actions while
>>> > others want different actions - then please implement key remapping in
>>> > the driver.
>>>
>>> That is exactly what I am trying to convince you. Without being able
>>> to tell one button event from the other, even just logically, how can
>>> I and other clients remap them?
>>
>> EVIOCSKEYCODE. You just need to wire wacom driver to support this ioctl.

Hold on. I was too concentrated on the buttons then. There are touch
rings (reported as ABS_WHEEL) on the tablet. How do we pass the raw
ring data to the user land and tell if that ABS_WHEEL is from the ring
or from a stylus' wheel? Should we add an ABS_RING then?

Also, if there is no tool on the tablet, which BTN_TOOL_* should we
use to report those buttons and strips/rings? They are not PEN, not
MOUSE, and not TOUCH. They are in fact an independent tool, like it or
not.

Ping
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