// SPDX-License-Identifier: GPL-2.0-only /* Copyright (c) 2023 Benjamin Tissoires */ #include "vmlinux.h" #include "hid_bpf.h" #include "hid_bpf_helpers.h" #include <bpf/bpf_tracing.h> #define VID_UGEE 0x28BD /* VID is shared with SinoWealth and Glorious and prob others */ #define PID_ARTIST_24 0x093A #define PID_ARTIST_24_PRO 0x092D HID_BPF_CONFIG( HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_UGEE, PID_ARTIST_24), HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_UGEE, PID_ARTIST_24_PRO) ); /* * We need to amend the report descriptor for the following: * - the device reports Eraser instead of using Secondary Barrel Switch * - the pen doesn't have a rubber tail, so basically we are removing any * eraser/invert bits */ static const __u8 fixed_rdesc[] = { 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, 0x00, // Collection (Physical) 10 0x09, 0x42, // Usage (Tip Switch) 12 0x09, 0x44, // Usage (Barrel Switch) 14 0x09, 0x5a, // Usage (Secondary Barrel Switch) 16 /* changed from 0x45 (Eraser) to 0x5a (Secondary Barrel Switch) */ 0x15, 0x00, // Logical Minimum (0) 18 0x25, 0x01, // Logical Maximum (1) 20 0x75, 0x01, // Report Size (1) 22 0x95, 0x03, // Report Count (3) 24 0x81, 0x02, // Input (Data,Var,Abs) 26 0x95, 0x02, // Report Count (2) 28 0x81, 0x03, // Input (Cnst,Var,Abs) 30 0x09, 0x32, // Usage (In Range) 32 0x95, 0x01, // Report Count (1) 34 0x81, 0x02, // Input (Data,Var,Abs) 36 0x95, 0x02, // Report Count (2) 38 0x81, 0x03, // Input (Cnst,Var,Abs) 40 0x75, 0x10, // Report Size (16) 42 0x95, 0x01, // Report Count (1) 44 0x35, 0x00, // Physical Minimum (0) 46 0xa4, // Push 48 0x05, 0x01, // Usage Page (Generic Desktop) 49 0x09, 0x30, // Usage (X) 51 0x65, 0x13, // Unit (EnglishLinear: in) 53 0x55, 0x0d, // Unit Exponent (-3) 55 0x46, 0xf0, 0x50, // Physical Maximum (20720) 57 0x26, 0xff, 0x7f, // Logical Maximum (32767) 60 0x81, 0x02, // Input (Data,Var,Abs) 63 0x09, 0x31, // Usage (Y) 65 0x46, 0x91, 0x2d, // Physical Maximum (11665) 67 0x26, 0xff, 0x7f, // Logical Maximum (32767) 70 0x81, 0x02, // Input (Data,Var,Abs) 73 0xb4, // Pop 75 0x09, 0x30, // Usage (Tip Pressure) 76 0x45, 0x00, // Physical Maximum (0) 78 0x26, 0xff, 0x1f, // Logical Maximum (8191) 80 0x81, 0x42, // Input (Data,Var,Abs,Null) 83 0x09, 0x3d, // Usage (X Tilt) 85 0x15, 0x81, // Logical Minimum (-127) 87 0x25, 0x7f, // Logical Maximum (127) 89 0x75, 0x08, // Report Size (8) 91 0x95, 0x01, // Report Count (1) 93 0x81, 0x02, // Input (Data,Var,Abs) 95 0x09, 0x3e, // Usage (Y Tilt) 97 0x15, 0x81, // Logical Minimum (-127) 99 0x25, 0x7f, // Logical Maximum (127) 101 0x81, 0x02, // Input (Data,Var,Abs) 103 0xc0, // End Collection 105 0xc0, // End Collection 106 }; #define TIP_SWITCH BIT(0) #define BARREL_SWITCH BIT(1) #define ERASER BIT(2) /* padding BIT(3) */ /* padding BIT(4) */ #define IN_RANGE BIT(5) /* padding BIT(6) */ /* padding BIT(7) */ #define U16(index) (data[index] | (data[index + 1] << 8)) SEC(HID_BPF_RDESC_FIXUP) int BPF_PROG(hid_fix_rdesc_xppen_artist24, struct hid_bpf_ctx *hctx) { __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 4096 /* size */); if (!data) return 0; /* EPERM check */ __builtin_memcpy(data, fixed_rdesc, sizeof(fixed_rdesc)); return sizeof(fixed_rdesc); } static __u8 prev_state = 0; /* * There are a few cases where the device is sending wrong event * sequences, all related to the second button (the pen doesn't * have an eraser switch on the tail end): * * whenever the second button gets pressed or released, an * out-of-proximity event is generated and then the firmware * compensate for the missing state (and the firmware uses * eraser for that button): * * - if the pen is in range, an extra out-of-range is sent * when the second button is pressed/released: * // Pen is in range * E: InRange * * // Second button is pressed * E: * E: Eraser InRange * * // Second button is released * E: * E: InRange * * This case is ignored by this filter, it's "valid" * and userspace knows how to deal with it, there are just * a few out-of-prox events generated, but the user doesn´t * see them. * * - if the pen is in contact, 2 extra events are added when * the second button is pressed/released: an out of range * and an in range: * * // Pen is in contact * E: TipSwitch InRange * * // Second button is pressed * E: <- false release, needs to be filtered out * E: Eraser InRange <- false release, needs to be filtered out * E: TipSwitch Eraser InRange * * // Second button is released * E: <- false release, needs to be filtered out * E: InRange <- false release, needs to be filtered out * E: TipSwitch InRange * */ SEC(HID_BPF_DEVICE_EVENT) int BPF_PROG(xppen_24_fix_eraser, struct hid_bpf_ctx *hctx) { __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 10 /* size */); __u8 current_state, changed_state; bool prev_tip; if (!data) return 0; /* EPERM check */ current_state = data[1]; /* if the state is identical to previously, early return */ if (current_state == prev_state) return 0; prev_tip = !!(prev_state & TIP_SWITCH); /* * Illegal transition: pen is in range with the tip pressed, and * it goes into out of proximity. * * Ideally we should hold the event, start a timer and deliver it * only if the timer ends, but we are not capable of that now. * * And it doesn't matter because when we are in such cases, this * means we are detecting a false release. */ if ((current_state & IN_RANGE) == 0) { if (prev_tip) return HID_IGNORE_EVENT; return 0; } /* * XOR to only set the bits that have changed between * previous and current state */ changed_state = prev_state ^ current_state; /* Store the new state for future processing */ prev_state = current_state; /* * We get both a tipswitch and eraser change in the same HID report: * this is not an authorized transition and is unlikely to happen * in real life. * This is likely to be added by the firmware to emulate the * eraser mode so we can skip the event. */ if ((changed_state & (TIP_SWITCH | ERASER)) == (TIP_SWITCH | ERASER)) /* we get both a tipswitch and eraser change at the same time */ return HID_IGNORE_EVENT; return 0; } HID_BPF_OPS(xppen_artist_24) = { .hid_rdesc_fixup = (void *)hid_fix_rdesc_xppen_artist24, .hid_device_event = (void *)xppen_24_fix_eraser, }; SEC("syscall") int probe(struct hid_bpf_probe_args *ctx) { /* * The device exports 3 interfaces. */ ctx->retval = ctx->rdesc_size != 107; if (ctx->retval) ctx->retval = -EINVAL; /* ensure the kernel isn't fixed already */ if (ctx->rdesc[17] != 0x45) /* Eraser */ ctx->retval = -EINVAL; return 0; } char _license[] SEC("license") = "GPL";
