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1// SPDX-License-Identifier: GPL-2.0-only2/* Copyright (c) 2024 Benjamin Tissoires3 */4 5#include "vmlinux.h"6#include "hid_bpf.h"7#include "hid_bpf_helpers.h"8#include <bpf/bpf_tracing.h>9 10#define VID_WACOM 0x056a11#define ART_PEN_ID 0x080412#define PID_INTUOS_PRO_2_M 0x035713 14HID_BPF_CONFIG(15 HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_WACOM, PID_INTUOS_PRO_2_M)16);17 18/*19 * This filter is here for the Art Pen stylus only:20 * - when used on some Wacom devices (see the list of attached PIDs), this pen21 * reports pressure every other events.22 * - to solve that, given that we know that the next event will be the same as23 * the current one, we can emulate a smoother pressure reporting by reporting24 * the mean of the previous value and the current one.25 *26 * We are effectively delaying the pressure by one event every other event, but27 * that's less of an annoyance compared to the chunkiness of the reported data.28 *29 * For example, let's assume the following set of events:30 * <Tip switch 0> <X 0> <Y 0> <Pressure 0 > <Tooltype 0x0804>31 * <Tip switch 1> <X 1> <Y 1> <Pressure 100 > <Tooltype 0x0804>32 * <Tip switch 1> <X 2> <Y 2> <Pressure 100 > <Tooltype 0x0804>33 * <Tip switch 1> <X 3> <Y 3> <Pressure 200 > <Tooltype 0x0804>34 * <Tip switch 1> <X 4> <Y 4> <Pressure 200 > <Tooltype 0x0804>35 * <Tip switch 0> <X 5> <Y 5> <Pressure 0 > <Tooltype 0x0804>36 *37 * The filter will report:38 * <Tip switch 0> <X 0> <Y 0> <Pressure 0 > <Tooltype 0x0804>39 * <Tip switch 1> <X 1> <Y 1> <Pressure * 50*> <Tooltype 0x0804>40 * <Tip switch 1> <X 2> <Y 2> <Pressure 100 > <Tooltype 0x0804>41 * <Tip switch 1> <X 3> <Y 3> <Pressure *150*> <Tooltype 0x0804>42 * <Tip switch 1> <X 4> <Y 4> <Pressure 200 > <Tooltype 0x0804>43 * <Tip switch 0> <X 5> <Y 5> <Pressure 0 > <Tooltype 0x0804>44 *45 */46 47struct wacom_params {48 __u16 pid;49 __u16 rdesc_len;50 __u8 report_id;51 __u8 report_len;52 struct {53 __u8 tip_switch;54 __u8 pressure;55 __u8 tool_type;56 } offsets;57};58 59/*60 * Multiple device can support the same stylus, so61 * we need to know which device has which offsets62 */63static const struct wacom_params devices[] = {64 {65 .pid = PID_INTUOS_PRO_2_M,66 .rdesc_len = 949,67 .report_id = 16,68 .report_len = 27,69 .offsets = {70 .tip_switch = 1,71 .pressure = 8,72 .tool_type = 25,73 },74 },75};76 77static struct wacom_params params = { 0 };78 79/* HID-BPF reports a 64 bytes chunk anyway, so this ensures80 * the verifier to know we are addressing the memory correctly81 */82#define PEN_REPORT_LEN 6483 84/* only odd frames are modified */85static bool odd;86 87static __u16 prev_pressure;88 89static inline void *get_bits(__u8 *data, unsigned int byte_offset)90{91 return data + byte_offset;92}93 94static inline __u16 *get_u16(__u8 *data, unsigned int offset)95{96 return (__u16 *)get_bits(data, offset);97}98 99static inline __u8 *get_u8(__u8 *data, unsigned int offset)100{101 return (__u8 *)get_bits(data, offset);102}103 104SEC(HID_BPF_DEVICE_EVENT)105int BPF_PROG(artpen_pressure_interpolate, struct hid_bpf_ctx *hctx)106{107 __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, PEN_REPORT_LEN /* size */);108 __u16 *pressure, *tool_type;109 __u8 *tip_switch;110 111 if (!data)112 return 0; /* EPERM check */113 114 if (data[0] != params.report_id ||115 params.offsets.tip_switch >= PEN_REPORT_LEN ||116 params.offsets.pressure >= PEN_REPORT_LEN - 1 ||117 params.offsets.tool_type >= PEN_REPORT_LEN - 1)118 return 0; /* invalid report or parameters */119 120 tool_type = get_u16(data, params.offsets.tool_type);121 if (*tool_type != ART_PEN_ID)122 return 0;123 124 tip_switch = get_u8(data, params.offsets.tip_switch);125 if ((*tip_switch & 0x01) == 0) {126 prev_pressure = 0;127 odd = true;128 return 0;129 }130 131 pressure = get_u16(data, params.offsets.pressure);132 133 if (odd)134 *pressure = (*pressure + prev_pressure) / 2;135 136 prev_pressure = *pressure;137 odd = !odd;138 139 return 0;140}141 142HID_BPF_OPS(wacom_artpen) = {143 .hid_device_event = (void *)artpen_pressure_interpolate,144};145 146SEC("syscall")147int probe(struct hid_bpf_probe_args *ctx)148{149 struct hid_bpf_ctx *hid_ctx;150 __u16 pid;151 int i;152 153 /* get a struct hid_device to access the actual pid of the device */154 hid_ctx = hid_bpf_allocate_context(ctx->hid);155 if (!hid_ctx) {156 ctx->retval = -ENODEV;157 return -1; /* EPERM check */158 }159 pid = hid_ctx->hid->product;160 161 ctx->retval = -EINVAL;162 163 /* Match the given device with the list of known devices */164 for (i = 0; i < ARRAY_SIZE(devices); i++) {165 const struct wacom_params *device = &devices[i];166 167 if (device->pid == pid && device->rdesc_len == ctx->rdesc_size) {168 params = *device;169 ctx->retval = 0;170 }171 }172 173 hid_bpf_release_context(hid_ctx);174 return 0;175}176 177char _license[] SEC("license") = "GPL";178