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