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Benjamin Tissoires
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HID: bpf: Add support for the XP-PEN Deco Mini 4
The XP-PEN Deco Mini 4 is a UGEE device with a frame with 6 buttons. Its pen has 2 buttons and supports pressure reporting. Fix their report descriptors and transform the frame button events to support it. Link: https://gitlab.freedesktop.org/libevdev/udev-hid-bpf/-/merge_requests/88 Signed-off-by: José Expósito <[email protected]> Link: https://patch.msgid.link/[email protected] Signed-off-by: Benjamin Tissoires <[email protected]>
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‎drivers/hid/bpf/progs/XPPen__DecoMini4.bpf.c

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

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