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Benjamin TissoiresJiri Kosina
Benjamin Tissoires
authored and
Jiri Kosina
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HID: bpf: Add support for the XP-Pen Deco 01 V3
This device needs a fix for the tilt range on the pen report descriptor and the usual conversion of the pad keys from the firmware's hardcoded keyboard shortcuts to actual pad buttons. Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net> Link: https://gitlab.freedesktop.org/libevdev/udev-hid-bpf/-/merge_requests/185 Signed-off-by: Benjamin Tissoires <bentiss@kernel.org> Signed-off-by: Jiri Kosina <jkosina@suse.com>
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‎drivers/hid/bpf/progs/XPPen__Deco01V3.bpf.c‎

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// SPDX-License-Identifier: GPL-2.0-only
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/* Copyright (c) 2025 Red Hat
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*/
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#include "vmlinux.h"
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#include "hid_bpf.h"
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#include "hid_bpf_helpers.h"
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#include "hid_report_helpers.h"
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#include <bpf/bpf_tracing.h>
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#define VID_UGEE 0x28BD /* VID is shared with SinoWealth and Glorious and prob others */
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#define PID_DECO_01_V3 0x0947
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HID_BPF_CONFIG(
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HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_UGEE, PID_DECO_01_V3),
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);
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/*
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* Default report descriptor reports:
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* - a report descriptor for the pad buttons, reported as key sequences
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* - a report descriptor for the pen
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* - a vendor-specific report descriptor
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*
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* The Pad report descriptor, see
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* https://gitlab.freedesktop.org/libevdev/udev-hid-bpf/-/issues/54
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*
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* # Report descriptor length: 102 bytes
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* 0x05, 0x01, // Usage Page (Generic Desktop) 0
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* 0x09, 0x02, // Usage (Mouse) 2
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* 0xa1, 0x01, // Collection (Application) 4
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* 0x85, 0x09, // Report ID (9) 6
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* 0x09, 0x01, // Usage (Pointer) 8
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* 0xa1, 0x00, // Collection (Physical) 10
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* 0x05, 0x09, // Usage Page (Button) 12
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* 0x19, 0x01, // UsageMinimum (1) 14
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* 0x29, 0x03, // UsageMaximum (3) 16
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* 0x15, 0x00, // Logical Minimum (0) 18
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* 0x25, 0x01, // Logical Maximum (1) 20
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* 0x95, 0x03, // Report Count (3) 22
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* 0x75, 0x01, // Report Size (1) 24
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* 0x81, 0x02, // Input (Data,Var,Abs) 26
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* 0x95, 0x05, // Report Count (5) 28
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* 0x81, 0x01, // Input (Cnst,Arr,Abs) 30
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* 0x05, 0x01, // Usage Page (Generic Desktop) 32
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* 0x09, 0x30, // Usage (X) 34
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* 0x09, 0x31, // Usage (Y) 36
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* 0x26, 0xff, 0x7f, // Logical Maximum (32767) 38
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* 0x95, 0x02, // Report Count (2) 41
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* 0x75, 0x10, // Report Size (16) 43
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* 0x81, 0x02, // Input (Data,Var,Abs) 45
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* 0x05, 0x0d, // Usage Page (Digitizers) 47
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* 0x09, 0x30, // Usage (Tip Pressure) 49
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* 0x26, 0xff, 0x07, // Logical Maximum (2047) 51
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* 0x95, 0x01, // Report Count (1) 54
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* 0x75, 0x10, // Report Size (16) 56
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* 0x81, 0x02, // Input (Data,Var,Abs) 58
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* 0xc0, // End Collection 60
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* 0xc0, // End Collection 61
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* 0x05, 0x01, // Usage Page (Generic Desktop) 62
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* 0x09, 0x06, // Usage (Keyboard) 64
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* 0xa1, 0x01, // Collection (Application) 66
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* 0x85, 0x06, // Report ID (6) 68
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* 0x05, 0x07, // Usage Page (Keyboard/Keypad) 70
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* 0x19, 0xe0, // UsageMinimum (224) 72
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* 0x29, 0xe7, // UsageMaximum (231) 74
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* 0x15, 0x00, // Logical Minimum (0) 76
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* 0x25, 0x01, // Logical Maximum (1) 78
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* 0x75, 0x01, // Report Size (1) 80
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* 0x95, 0x08, // Report Count (8) 82
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* 0x81, 0x02, // Input (Data,Var,Abs) 84
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* 0x05, 0x07, // Usage Page (Keyboard/Keypad) 86
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* 0x19, 0x00, // UsageMinimum (0) 88
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* 0x29, 0xff, // UsageMaximum (255) 90
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* 0x26, 0xff, 0x00, // Logical Maximum (255) 92
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* 0x75, 0x08, // Report Size (8) 95
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* 0x95, 0x06, // Report Count (6) 97
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* 0x81, 0x00, // Input (Data,Arr,Abs) 99
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* 0xc0, // End Collection 101
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*
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* And key events for buttons top->bottom are:
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* Buttons released: 06 00 00 00 00 00 00 00
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* Button1: 06 00 05 00 00 00 00 00 -> b
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* Button2: 06 00 08 00 00 00 00 00 -> e
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* Button3: 06 04 00 00 00 00 00 00 -> LAlt
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* Button4: 06 00 2c 00 00 00 00 00 -> Space
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* Button5: 06 01 16 00 00 00 00 00 -> LControl + s
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* Button6: 06 01 1d 00 00 00 00 00 -> LControl + z
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* Button7: 06 01 57 00 00 00 00 00 -> LControl + Keypad Plus
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* Button8: 06 01 56 00 00 00 00 00 -> LControl + Keypad Dash
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*
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* When multiple buttons are pressed at the same time, the values used to
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* identify the buttons are identical, but they appear in different bytes of the
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* record. For example, when button 2 (0x08) and button 1 (0x05) are pressed,
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* this is the report:
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*
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* Buttons 2 and 1: 06 00 08 05 00 00 00 00 -> e + b
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*
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* Buttons 1, 2, 4, 5 and 6 can be matched by finding their values in the
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* report.
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*
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* Button 3 is pressed when the 3rd bit is 1. For example, pressing buttons 3
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* and 5 generates this report:
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*
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* Buttons 3 and 5: 06 05 16 00 00 00 00 00 -> LControl + LAlt + s
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* -- --
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* | |
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* | `- Button 5 (0x16)
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* `- 0x05 = 0101. Button 3 is pressed
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* ^
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*
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* pad_buttons contains a list of buttons that can be matched in
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* HID_BPF_DEVICE_EVENT. Button 3 as it has a dedicated bit.
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*
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*
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* The Pen report descriptor announces a wrong tilt range:
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*
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* Report descriptor length: 109 bytes
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* 0x05, 0x0d, // Usage Page (Digitizers) 0
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* 0x09, 0x02, // Usage (Pen) 2
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* 0xa1, 0x01, // Collection (Application) 4
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* 0x85, 0x07, // Report ID (7) 6
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* 0x09, 0x20, // Usage (Stylus) 8
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* 0xa1, 0x01, // Collection (Application) 10
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* 0x09, 0x42, // Usage (Tip Switch) 12
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* 0x09, 0x44, // Usage (Barrel Switch) 14
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* 0x09, 0x45, // Usage (Eraser) 16
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* 0x09, 0x3c, // Usage (Invert) 18
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* 0x15, 0x00, // Logical Minimum (0) 20
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* 0x25, 0x01, // Logical Maximum (1) 22
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* 0x75, 0x01, // Report Size (1) 24
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* 0x95, 0x04, // Report Count (4) 26
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* 0x81, 0x02, // Input (Data,Var,Abs) 28
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* 0x95, 0x01, // Report Count (1) 30
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* 0x81, 0x03, // Input (Cnst,Var,Abs) 32
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* 0x09, 0x32, // Usage (In Range) 34
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* 0x95, 0x01, // Report Count (1) 36
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* 0x81, 0x02, // Input (Data,Var,Abs) 38
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* 0x95, 0x02, // Report Count (2) 40
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* 0x81, 0x03, // Input (Cnst,Var,Abs) 42
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* 0x75, 0x10, // Report Size (16) 44
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* 0x95, 0x01, // Report Count (1) 46
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* 0x35, 0x00, // Physical Minimum (0) 48
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* 0xa4, // Push 50
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* 0x05, 0x01, // Usage Page (Generic Desktop) 51
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* 0x09, 0x30, // Usage (X) 53
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* 0x65, 0x13, // Unit (EnglishLinear: in) 55
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* 0x55, 0x0d, // Unit Exponent (-3) 57
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* 0x46, 0x10, 0x27, // Physical Maximum (10000) 59
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* 0x26, 0xff, 0x7f, // Logical Maximum (32767) 62
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* 0x81, 0x02, // Input (Data,Var,Abs) 65
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* 0x09, 0x31, // Usage (Y) 67
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* 0x46, 0x6a, 0x18, // Physical Maximum (6250) 69
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* 0x26, 0xff, 0x7f, // Logical Maximum (32767) 72
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* 0x81, 0x02, // Input (Data,Var,Abs) 75
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* 0xb4, // Pop 77
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* 0x09, 0x30, // Usage (X) 78
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* 0x45, 0x00, // Physical Maximum (0) 80
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* 0x26, 0xff, 0x3f, // Logical Maximum (16383) 82
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* 0x81, 0x42, // Input (Data,Var,Abs,Null) 85
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* 0x09, 0x3d, // Usage (Start) 87
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* 0x15, 0x81, // Logical Minimum (-127) 89 <- Change from -127 to -60
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* 0x25, 0x7f, // Logical Maximum (127) 91 <- Change from 127 to 60
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* 0x75, 0x08, // Report Size (8) 93
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* 0x95, 0x01, // Report Count (1) 95
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* 0x81, 0x02, // Input (Data,Var,Abs) 97
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* 0x09, 0x3e, // Usage (Select) 99
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* 0x15, 0x81, // Logical Minimum (-127) 101 <- Change from -127 to -60
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* 0x25, 0x7f, // Logical Maximum (127) 103 <- Change from 127 to 60
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* 0x81, 0x02, // Input (Data,Var,Abs) 105
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* 0xc0, // End Collection 107
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* 0xc0, // End Collection 108
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*/
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#define PEN_REPORT_DESCRIPTOR_LENGTH 109
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#define PAD_REPORT_DESCRIPTOR_LENGTH 102
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#define PAD_REPORT_LENGTH 8
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#define PAD_REPORT_ID 6
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#define PAD_NUM_BUTTONS 8
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static const __u8 fixed_rdesc_pad[] = {
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UsagePage_GenericDesktop
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Usage_GD_Keypad
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CollectionApplication(
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// Byte 0 in report is the report ID
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ReportId(PAD_REPORT_ID)
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ReportCount(1)
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ReportSize(8)
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UsagePage_Digitizers
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Usage_Dig_TabletFunctionKeys
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CollectionPhysical(
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// Byte 1 is the button state
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UsagePage_Button
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UsageMinimum_i8(0x01)
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UsageMaximum_i8(PAD_NUM_BUTTONS)
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LogicalMinimum_i8(0x0)
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LogicalMaximum_i8(0x1)
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ReportCount(PAD_NUM_BUTTONS)
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ReportSize(1)
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Input(Var|Abs)
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// Byte 2 in report - just exists so we get to be a tablet pad
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UsagePage_Digitizers
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Usage_Dig_BarrelSwitch // BTN_STYLUS
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ReportCount(1)
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ReportSize(1)
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Input(Var|Abs)
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ReportCount(7) // padding
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Input(Const)
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// Bytes 3/4 in report - just exists so we get to be a tablet pad
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UsagePage_GenericDesktop
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Usage_GD_X
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Usage_GD_Y
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ReportCount(2)
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ReportSize(8)
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Input(Var|Abs)
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// Byte 5-7 are padding so we match the original report lengtth
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ReportCount(3)
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ReportSize(8)
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Input(Const)
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)
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)
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};
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SEC(HID_BPF_RDESC_FIXUP)
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int BPF_PROG(xppen_deco01v3_rdesc_fixup, struct hid_bpf_ctx *hctx)
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{
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__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, HID_MAX_DESCRIPTOR_SIZE /* size */);
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const __u8 wrong_logical_range[] = {0x15, 0x81, 0x25, 0x7f};
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const __u8 correct_logical_range[] = {0x15, 0xc4, 0x25, 0x3c};
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if (!data)
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return 0; /* EPERM check */
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switch (hctx->size) {
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case PAD_REPORT_DESCRIPTOR_LENGTH:
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__builtin_memcpy(data, fixed_rdesc_pad, sizeof(fixed_rdesc_pad));
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return sizeof(fixed_rdesc_pad);
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case PEN_REPORT_DESCRIPTOR_LENGTH:
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if (__builtin_memcmp(&data[89], wrong_logical_range,
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sizeof(wrong_logical_range)) == 0)
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__builtin_memcpy(&data[89], correct_logical_range,
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sizeof(correct_logical_range));
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if (__builtin_memcmp(&data[101], wrong_logical_range,
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sizeof(wrong_logical_range)) == 0)
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__builtin_memcpy(&data[101], correct_logical_range,
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sizeof(correct_logical_range));
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break;
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}
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return 0;
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}
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SEC(HID_BPF_DEVICE_EVENT)
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int BPF_PROG(xppen_deco01v3_device_event, struct hid_bpf_ctx *hctx)
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{
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static const __u8 pad_buttons[] = { 0x05, 0x08, 0x00, 0x2c, 0x16, 0x1d, 0x57, 0x56 };
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__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, PAD_REPORT_LENGTH /* size */);
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if (!data)
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return 0; /* EPERM check */
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if (data[0] == PAD_REPORT_ID) {
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__u8 button_mask = 0;
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size_t d, b;
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/* data[1] stores the status of BTN_2 in the 3rd bit*/
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if (data[1] & BIT(2))
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button_mask |= BIT(2);
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/* The rest of the descriptor stores the buttons as in pad_buttons */
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for (d = 2; d < 8; d++) {
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for (b = 0; b < sizeof(pad_buttons); b++) {
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if (data[d] != 0 && data[d] == pad_buttons[b])
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button_mask |= BIT(b);
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}
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}
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__u8 report[8] = {PAD_REPORT_ID, button_mask, 0x00};
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__builtin_memcpy(data, report, sizeof(report));
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}
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return 0;
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}
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HID_BPF_OPS(xppen_deco01v3) = {
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.hid_rdesc_fixup = (void *)xppen_deco01v3_rdesc_fixup,
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.hid_device_event = (void *)xppen_deco01v3_device_event,
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};
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SEC("syscall")
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int probe(struct hid_bpf_probe_args *ctx)
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{
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switch (ctx->rdesc_size) {
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case PAD_REPORT_DESCRIPTOR_LENGTH:
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case PEN_REPORT_DESCRIPTOR_LENGTH:
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ctx->retval = 0;
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break;
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default:
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ctx->retval = -EINVAL;
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}
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return 0;
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}
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char _license[] SEC("license") = "GPL";

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