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// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2024 José Expósito
*/
#include "vmlinux.h"
#include "hid_bpf.h"
#include "hid_bpf_helpers.h"
#include <bpf/bpf_tracing.h>
#define VID_UGEE 0x28BD
#define PID_DECO_MINI_4 0x0929
#define RDESC_SIZE_PAD 177
#define RDESC_SIZE_PEN 109
#define PAD_REPORT_ID 0x06
/*
* XP-Pen devices return a descriptor with the values the driver should use when
* one of its interfaces is queried. For this device the descriptor is:
*
* 0E 03 60 4F 88 3B 06 00 FF 1F D8 13
* ----- ----- ----- -----
* | | | |
* | | | `- Resolution: 5080 (13d8)
* | | `- Maximum pressure: 8191 (1FFF)
* | `- Logical maximum Y: 15240 (3B88)
* `- Logical maximum X: 20320 (4F60)
*
* The physical maximum is calculated as (logical_max * 1000) / resolution.
*/
#define LOGICAL_MAX_X 0x60, 0x4F
#define LOGICAL_MAX_Y 0x88, 0x3B
#define PHYSICAL_MAX_X 0xA0, 0x0F
#define PHYSICAL_MAX_Y 0xB8, 0x0B
#define PRESSURE_MAX 0xFF, 0x1F
HID_BPF_CONFIG(
HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_UGEE, PID_DECO_MINI_4)
);
/*
* The tablet send these values when the pad buttons are pressed individually:
*
* Buttons released: 06 00 00 00 00 00 00 00
* Button 1: 06 00 05 00 00 00 00 00 -> b
* Button 2: 06 00 08 00 00 00 00 00 -> e
* Button 3: 06 04 00 00 00 00 00 00 -> LAlt
* Button 4: 06 00 2c 00 00 00 00 00 -> Space
* Button 5: 06 01 16 00 00 00 00 00 -> LControl + s
* Button 6: 06 01 1d 00 00 00 00 00 -> LControl + z
*
* 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.
*/
static const __u8 pad_buttons[] = { 0x05, 0x08, 0x00, 0x2C, 0x16, 0x1D };
static const __u8 fixed_pad_rdesc[] = {
0x05, 0x01, /* Usage Page (Desktop), */
0x09, 0x07, /* Usage (Keypad), */
0xA1, 0x01, /* Collection (Application), */
0x85, 0x06, /* Report ID (6), */
0x05, 0x0D, /* Usage Page (Digitizer), */
0x09, 0x39, /* Usage (Tablet Function Keys), */
0xA0, /* Collection (Physical), */
0x05, 0x09, /* Usage Page (Button), */
0x75, 0x01, /* Report Size (1), */
0x95, 0x06, /* Report Count (6), */
0x19, 0x01, /* Usage Minimum (01h), */
0x29, 0x06, /* Usage Maximum (06h), */
0x14, /* Logical Minimum (0), */
0x25, 0x01, /* Logical Maximum (1), */
0x81, 0x02, /* Input (Variable), */
0x95, 0x32, /* Report Count (50), */
0x81, 0x01, /* Input (Constant), */
0xC0, /* End Collection, */
0xC0 /* End Collection */
};
static const __u8 fixed_pen_rdesc[] = {
0x05, 0x0d, /* Usage Page (Digitizers), */
0x09, 0x01, /* Usage (Digitizer), */
0xa1, 0x01, /* Collection (Application), */
0x85, 0x07, /* Report ID (7), */
0x09, 0x20, /* Usage (Stylus), */
0xa1, 0x00, /* Collection (Physical), */
0x09, 0x42, /* Usage (Tip Switch), */
0x09, 0x44, /* Usage (Barrel Switch), */
0x09, 0x46, /* Usage (Tablet Pick), */
0x75, 0x01, /* Report Size (1), */
0x95, 0x03, /* Report Count (3), */
0x14, /* Logical Minimum (0), */
0x25, 0x01, /* Logical Maximum (1), */
0x81, 0x02, /* Input (Variable), */
0x95, 0x02, /* Report Count (2), */
0x81, 0x03, /* Input (Constant, Variable), */
0x09, 0x32, /* Usage (In Range), */
0x95, 0x01, /* Report Count (1), */
0x81, 0x02, /* Input (Variable), */
0x95, 0x02, /* Report Count (2), */
0x81, 0x03, /* Input (Constant, Variable), */
0x75, 0x10, /* Report Size (16), */
0x95, 0x01, /* Report Count (1), */
0x35, 0x00, /* Physical Minimum (0), */
0xa4, /* Push, */
0x05, 0x01, /* Usage Page (Desktop), */
0x09, 0x30, /* Usage (X), */
0x65, 0x13, /* Unit (Inch), */
0x55, 0x0d, /* Unit Exponent (-3), */
0x26, LOGICAL_MAX_X, /* Logical Maximum, */
0x46, PHYSICAL_MAX_X, /* Physical Maximum, */
0x81, 0x02, /* Input (Variable), */
0x09, 0x31, /* Usage (Y), */
0x26, LOGICAL_MAX_Y, /* Logical Maximum, */
0x46, PHYSICAL_MAX_Y, /* Physical Maximum, */
0x81, 0x02, /* Input (Variable), */
0xb4, /* Pop, */
0x09, 0x30, /* Usage (Tip Pressure), */
0x45, 0x00, /* Physical Maximum (0), */
0x26, PRESSURE_MAX, /* Logical Maximum, */
0x75, 0x0D, /* Report Size (13), */
0x95, 0x01, /* Report Count (1), */
0x81, 0x02, /* Input (Variable), */
0x75, 0x01, /* Report Size (1), */
0x95, 0x13, /* Report Count (19), */
0x81, 0x01, /* Input (Constant), */
0xc0, /* End Collection, */
0xc0, /* End Collection */
};
static const size_t fixed_pad_rdesc_size = sizeof(fixed_pad_rdesc);
static const size_t fixed_pen_rdesc_size = sizeof(fixed_pen_rdesc);
SEC(HID_BPF_RDESC_FIXUP)
int BPF_PROG(hid_rdesc_fixup_xppen_deco_mini_4, struct hid_bpf_ctx *hctx)
{
__u8 *data = hid_bpf_get_data(hctx, 0, HID_MAX_DESCRIPTOR_SIZE);
if (!data)
return 0; /* EPERM check */
if (hctx->size == RDESC_SIZE_PAD) {
__builtin_memcpy(data, fixed_pad_rdesc, fixed_pad_rdesc_size);
return fixed_pad_rdesc_size;
} else if (hctx->size == RDESC_SIZE_PEN) {
__builtin_memcpy(data, fixed_pen_rdesc, fixed_pen_rdesc_size);
return fixed_pen_rdesc_size;
}
return 0;
}
SEC(HID_BPF_DEVICE_EVENT)
int BPF_PROG(hid_device_event_xppen_deco_mini_4, struct hid_bpf_ctx *hctx)
{
__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 8 /* size */);
__u8 button_mask = 0;
int d, b;
if (!data)
return 0; /* EPERM check */
if (data[0] != PAD_REPORT_ID)
return 0;
/* 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(deco_mini_4) = {
.hid_device_event = (void *)hid_device_event_xppen_deco_mini_4,
.hid_rdesc_fixup = (void *)hid_rdesc_fixup_xppen_deco_mini_4,
};
SEC("syscall")
int probe(struct hid_bpf_probe_args *ctx)
{
/*
* The device has 2 modes: The compatibility mode, enabled by default,
* and the raw mode, that can be activated by sending a buffer of magic
* data to a certain USB endpoint.
*
* Depending on the mode, different interfaces of the device are used:
* - First interface: Pad in compatibility mode
* - Second interface: Pen in compatibility mode
* - Third interface: Only used in raw mode
*
* We'll use the device in compatibility mode.
*/
ctx->retval = ctx->rdesc_size != RDESC_SIZE_PAD &&
ctx->rdesc_size != RDESC_SIZE_PEN;
if (ctx->retval)
ctx->retval = -EINVAL;
return 0;
}
char _license[] SEC("license") = "GPL";
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