linux-kernel - Re: Requesting your attention and expertise regarding a Tablet/Kernel issue

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Date:   Sat, 4 Nov 2023 07:46:48 +0700
From:   Bagas Sanjaya <bagasdotme@...il.com>
To:     Illia Ostapyshyn <ostapyshyn@....uni-hannover.de>, jkosina@...e.cz
Cc:     benjamin.tissoires@...hat.com, davidrevoy@...tonmail.com,
        jason.gerecke@...om.com, jose.exposito89@...il.com,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        nils@...sfuhler.de, peter.hutterer@...-t.net, ping.cheng@...om.com
Subject: Re: Requesting your attention and expertise regarding a
 Tablet/Kernel issue

On Fri, Nov 03, 2023 at 09:05:25PM +0100, Illia Ostapyshyn wrote:
> Hello David, Hello Jiri,
> 
> The XP-Pen hardware reports the Eraser usage for the upper stylus button.
> Generally, styli report Invert usages when erasing, as described in [1].
> XP-Pen digitizers, however, tend to omit them.
> 
> The generic driver maps the Eraser usage to BTN_TOUCH and the Invert
> usage to BTN_TOOL_RUBBER.  Pens conforming to [1] send the Invert usage
> first (switching the tool to BTN_TOOL_RUBBER) followed by Eraser, which
> appears in userspace as a BTN_TOUCH event with the rubber tool set.
> 
> Due to an oversight, devices not reporting Invert had the BTN_TOOL_RUBBER
> event masked.  This has caused the kernel to send only BTN_TOUCH events
> without the tool switch when erasing.
> 
> The situation got worse with refactoring done in 87562fcd1342.  An eraser
> without Invert caused the hidinput_hid_event state machine to get stuck
> with BTN_TOOL_RUBBER internally (due to it being masked).  For the
> userspace, this looked as if the pen was never hovering again, rendering
> it unusable until the next reset.  276e14e6c3 fixes this by adding
> support for digitizers that do not report Invert usages when erasing.
> 
> ---
> 
> David, we are sorry that our patch broke your workflow.  However,
> forwarding hardware events *as-is* to the userspace has always been the
> intended behavior, with a kernel bug preventing it so far.  You can still
> remap the eraser button to a right click using xsetwacom:
> 
> xsetwacom set "UGTABLET 24 inch PenDisplay eraser" "Button" "1" "3"
> 
> Replace the device name with the corresponding *eraser* device from
> "xsetwacom list devices".  You can also do this with "xinput set-button-map",
> which works for libinput as well.  We have tested this with several
> XP-Pen devices, including Artist 24.
> 
> [1] https://learn.microsoft.com/en-us/windows-hardware/design/component-guidelines/windows-pen-states

Thanks for the explanation!

-- 
An old man doll... just what I always wanted! - Clara

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