1 // SPDX-License-Identifier: GPL-2.0-only 2 /* Copyright (c) 2023 Benjamin Tissoires 3 */ 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_UGEE 0x28BD /* VID is shared with SinoWealth and Glorious and prob others */ 11 #define PID_ARTIST_24 0x093A 12 #define PID_ARTIST_24_PRO 0x092D 13 14 HID_BPF_CONFIG( 15 HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_UGEE, PID_ARTIST_24), 16 HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_UGEE, PID_ARTIST_24_PRO) 17 ); 18 19 /* 20 * We need to amend the report descriptor for the following: 21 * - the device reports Eraser instead of using Secondary Barrel Switch 22 * - the pen doesn't have a rubber tail, so basically we are removing any 23 * eraser/invert bits 24 */ 25 static const __u8 fixed_rdesc[] = { 26 0x05, 0x0d, // Usage Page (Digitizers) 0 27 0x09, 0x02, // Usage (Pen) 2 28 0xa1, 0x01, // Collection (Application) 4 29 0x85, 0x07, // Report ID (7) 6 30 0x09, 0x20, // Usage (Stylus) 8 31 0xa1, 0x00, // Collection (Physical) 10 32 0x09, 0x42, // Usage (Tip Switch) 12 33 0x09, 0x44, // Usage (Barrel Switch) 14 34 0x09, 0x5a, // Usage (Secondary Barrel Switch) 16 /* changed from 0x45 (Eraser) to 0x5a (Secondary Barrel Switch) */ 35 0x15, 0x00, // Logical Minimum (0) 18 36 0x25, 0x01, // Logical Maximum (1) 20 37 0x75, 0x01, // Report Size (1) 22 38 0x95, 0x03, // Report Count (3) 24 39 0x81, 0x02, // Input (Data,Var,Abs) 26 40 0x95, 0x02, // Report Count (2) 28 41 0x81, 0x03, // Input (Cnst,Var,Abs) 30 42 0x09, 0x32, // Usage (In Range) 32 43 0x95, 0x01, // Report Count (1) 34 44 0x81, 0x02, // Input (Data,Var,Abs) 36 45 0x95, 0x02, // Report Count (2) 38 46 0x81, 0x03, // Input (Cnst,Var,Abs) 40 47 0x75, 0x10, // Report Size (16) 42 48 0x95, 0x01, // Report Count (1) 44 49 0x35, 0x00, // Physical Minimum (0) 46 50 0xa4, // Push 48 51 0x05, 0x01, // Usage Page (Generic Desktop) 49 52 0x09, 0x30, // Usage (X) 51 53 0x65, 0x13, // Unit (EnglishLinear: in) 53 54 0x55, 0x0d, // Unit Exponent (-3) 55 55 0x46, 0xf0, 0x50, // Physical Maximum (20720) 57 56 0x26, 0xff, 0x7f, // Logical Maximum (32767) 60 57 0x81, 0x02, // Input (Data,Var,Abs) 63 58 0x09, 0x31, // Usage (Y) 65 59 0x46, 0x91, 0x2d, // Physical Maximum (11665) 67 60 0x26, 0xff, 0x7f, // Logical Maximum (32767) 70 61 0x81, 0x02, // Input (Data,Var,Abs) 73 62 0xb4, // Pop 75 63 0x09, 0x30, // Usage (Tip Pressure) 76 64 0x45, 0x00, // Physical Maximum (0) 78 65 0x26, 0xff, 0x1f, // Logical Maximum (8191) 80 66 0x81, 0x42, // Input (Data,Var,Abs,Null) 83 67 0x09, 0x3d, // Usage (X Tilt) 85 68 0x15, 0x81, // Logical Minimum (-127) 87 69 0x25, 0x7f, // Logical Maximum (127) 89 70 0x75, 0x08, // Report Size (8) 91 71 0x95, 0x01, // Report Count (1) 93 72 0x81, 0x02, // Input (Data,Var,Abs) 95 73 0x09, 0x3e, // Usage (Y Tilt) 97 74 0x15, 0x81, // Logical Minimum (-127) 99 75 0x25, 0x7f, // Logical Maximum (127) 101 76 0x81, 0x02, // Input (Data,Var,Abs) 103 77 0xc0, // End Collection 105 78 0xc0, // End Collection 106 79 }; 80 81 #define TIP_SWITCH BIT(0) 82 #define BARREL_SWITCH BIT(1) 83 #define ERASER BIT(2) 84 /* padding BIT(3) */ 85 /* padding BIT(4) */ 86 #define IN_RANGE BIT(5) 87 /* padding BIT(6) */ 88 /* padding BIT(7) */ 89 90 #define U16(index) (data[index] | (data[index + 1] << 8)) 91 92 SEC(HID_BPF_RDESC_FIXUP) 93 int BPF_PROG(hid_fix_rdesc_xppen_artist24, struct hid_bpf_ctx *hctx) 94 { 95 __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 4096 /* size */); 96 97 if (!data) 98 return 0; /* EPERM check */ 99 100 __builtin_memcpy(data, fixed_rdesc, sizeof(fixed_rdesc)); 101 102 return sizeof(fixed_rdesc); 103 } 104 105 static __u8 prev_state = 0; 106 107 /* 108 * There are a few cases where the device is sending wrong event 109 * sequences, all related to the second button (the pen doesn't 110 * have an eraser switch on the tail end): 111 * 112 * whenever the second button gets pressed or released, an 113 * out-of-proximity event is generated and then the firmware 114 * compensate for the missing state (and the firmware uses 115 * eraser for that button): 116 * 117 * - if the pen is in range, an extra out-of-range is sent 118 * when the second button is pressed/released: 119 * // Pen is in range 120 * E: InRange 121 * 122 * // Second button is pressed 123 * E: 124 * E: Eraser InRange 125 * 126 * // Second button is released 127 * E: 128 * E: InRange 129 * 130 * This case is ignored by this filter, it's "valid" 131 * and userspace knows how to deal with it, there are just 132 * a few out-of-prox events generated, but the user doesn´t 133 * see them. 134 * 135 * - if the pen is in contact, 2 extra events are added when 136 * the second button is pressed/released: an out of range 137 * and an in range: 138 * 139 * // Pen is in contact 140 * E: TipSwitch InRange 141 * 142 * // Second button is pressed 143 * E: <- false release, needs to be filtered out 144 * E: Eraser InRange <- false release, needs to be filtered out 145 * E: TipSwitch Eraser InRange 146 * 147 * // Second button is released 148 * E: <- false release, needs to be filtered out 149 * E: InRange <- false release, needs to be filtered out 150 * E: TipSwitch InRange 151 * 152 */ 153 SEC(HID_BPF_DEVICE_EVENT) 154 int BPF_PROG(xppen_24_fix_eraser, struct hid_bpf_ctx *hctx) 155 { 156 __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 10 /* size */); 157 __u8 current_state, changed_state; 158 bool prev_tip; 159 160 if (!data) 161 return 0; /* EPERM check */ 162 163 current_state = data[1]; 164 165 /* if the state is identical to previously, early return */ 166 if (current_state == prev_state) 167 return 0; 168 169 prev_tip = !!(prev_state & TIP_SWITCH); 170 171 /* 172 * Illegal transition: pen is in range with the tip pressed, and 173 * it goes into out of proximity. 174 * 175 * Ideally we should hold the event, start a timer and deliver it 176 * only if the timer ends, but we are not capable of that now. 177 * 178 * And it doesn't matter because when we are in such cases, this 179 * means we are detecting a false release. 180 */ 181 if ((current_state & IN_RANGE) == 0) { 182 if (prev_tip) 183 return HID_IGNORE_EVENT; 184 return 0; 185 } 186 187 /* 188 * XOR to only set the bits that have changed between 189 * previous and current state 190 */ 191 changed_state = prev_state ^ current_state; 192 193 /* Store the new state for future processing */ 194 prev_state = current_state; 195 196 /* 197 * We get both a tipswitch and eraser change in the same HID report: 198 * this is not an authorized transition and is unlikely to happen 199 * in real life. 200 * This is likely to be added by the firmware to emulate the 201 * eraser mode so we can skip the event. 202 */ 203 if ((changed_state & (TIP_SWITCH | ERASER)) == (TIP_SWITCH | ERASER)) /* we get both a tipswitch and eraser change at the same time */ 204 return HID_IGNORE_EVENT; 205 206 return 0; 207 } 208 209 HID_BPF_OPS(xppen_artist_24) = { 210 .hid_rdesc_fixup = (void *)hid_fix_rdesc_xppen_artist24, 211 .hid_device_event = (void *)xppen_24_fix_eraser, 212 }; 213 214 SEC("syscall") 215 int probe(struct hid_bpf_probe_args *ctx) 216 { 217 /* 218 * The device exports 3 interfaces. 219 */ 220 ctx->retval = ctx->rdesc_size != 107; 221 if (ctx->retval) 222 ctx->retval = -EINVAL; 223 224 /* ensure the kernel isn't fixed already */ 225 if (ctx->rdesc[17] != 0x45) /* Eraser */ 226 ctx->retval = -EINVAL; 227 228 return 0; 229 } 230 231 char _license[] SEC("license") = "GPL"; 232