| // SPDX-License-Identifier: GPL-2.0-only |
| /* Copyright (c) 2025 Red Hat |
| */ |
| |
| #include "vmlinux.h" |
| #include "hid_bpf.h" |
| #include "hid_bpf_helpers.h" |
| #include <bpf/bpf_tracing.h> |
| |
| #define VID_WALTOP 0x172F |
| #define PID_BATTERYLESS_TABLET 0x0505 |
| |
| HID_BPF_CONFIG( |
| HID_DEVICE(BUS_USB, HID_GROUP_ANY, VID_WALTOP, PID_BATTERYLESS_TABLET) |
| ); |
| |
| #define EXPECTED_RDESC_SIZE 335 |
| #define PEN_REPORT_ID 16 |
| |
| #define TIP_SWITCH BIT(0) |
| #define BARREL_SWITCH BIT(1) |
| #define SECONDARY_BARREL_SWITCH BIT(5) |
| |
| static __u8 last_button_state; |
| |
| static const __u8 fixed_rdesc[] = { |
| 0x05, 0x01, // Usage Page (Generic Desktop) |
| 0x09, 0x02, // Usage (Mouse) |
| 0xa1, 0x01, // Collection (Application) |
| 0x85, 0x01, // Report ID (1) |
| 0x09, 0x01, // Usage (Pointer) |
| 0xa1, 0x00, // Collection (Physical) |
| 0x05, 0x09, // Usage Page (Button) |
| 0x19, 0x01, // Usage Minimum (1) |
| 0x29, 0x05, // Usage Maximum (5) |
| 0x15, 0x00, // Logical Minimum (0) |
| 0x25, 0x01, // Logical Maximum (1) |
| 0x75, 0x01, // Report Size (1) |
| 0x95, 0x05, // Report Count (5) |
| 0x81, 0x02, // Input (Data,Var,Abs) |
| 0x75, 0x03, // Report Size (3) |
| 0x95, 0x01, // Report Count (1) |
| 0x81, 0x03, // Input (Cnst,Var,Abs) |
| 0x05, 0x01, // Usage Page (Generic Desktop) |
| 0x09, 0x30, // Usage (X) |
| 0x09, 0x31, // Usage (Y) |
| 0x09, 0x38, // Usage (Wheel) |
| 0x15, 0x81, // Logical Minimum (-127) |
| 0x25, 0x7f, // Logical Maximum (127) |
| 0x75, 0x08, // Report Size (8) |
| 0x95, 0x03, // Report Count (3) |
| 0x81, 0x06, // Input (Data,Var,Rel) |
| 0x05, 0x0c, // Usage Page (Consumer) |
| 0x15, 0x81, // Logical Minimum (-127) |
| 0x25, 0x7f, // Logical Maximum (127) |
| 0x75, 0x08, // Report Size (8) |
| 0x95, 0x01, // Report Count (1) |
| 0x0a, 0x38, 0x02, // Usage (AC Pan) |
| 0x81, 0x06, // Input (Data,Var,Rel) |
| 0xc0, // End Collection |
| 0xc0, // End Collection |
| 0x05, 0x0d, // Usage Page (Digitizers) |
| 0x09, 0x02, // Usage (Pen) |
| 0xa1, 0x01, // Collection (Application) |
| 0x85, 0x02, // Report ID (2) |
| 0x09, 0x20, // Usage (Stylus) |
| 0xa1, 0x00, // Collection (Physical) |
| 0x09, 0x00, // Usage (0x0000) |
| 0x15, 0x00, // Logical Minimum (0) |
| 0x26, 0xff, 0x00, // Logical Maximum (255) |
| 0x75, 0x08, // Report Size (8) |
| 0x95, 0x09, // Report Count (9) |
| 0x81, 0x02, // Input (Data,Var,Abs) |
| 0x09, 0x3f, // Usage (Azimuth) |
| 0x09, 0x40, // Usage (Altitude) |
| 0x15, 0x00, // Logical Minimum (0) |
| 0x26, 0xff, 0x00, // Logical Maximum (255) |
| 0x75, 0x08, // Report Size (8) |
| 0x95, 0x02, // Report Count (2) |
| 0xb1, 0x02, // Feature (Data,Var,Abs) |
| 0xc0, // End Collection |
| 0x85, 0x05, // Report ID (5) |
| 0x05, 0x0d, // Usage Page (Digitizers) |
| 0x09, 0x20, // Usage (Stylus) |
| 0xa1, 0x00, // Collection (Physical) |
| 0x09, 0x00, // Usage (0x0000) |
| 0x15, 0x00, // Logical Minimum (0) |
| 0x26, 0xff, 0x00, // Logical Maximum (255) |
| 0x75, 0x08, // Report Size (8) |
| 0x95, 0x07, // Report Count (7) |
| 0x81, 0x02, // Input (Data,Var,Abs) |
| 0xc0, // End Collection |
| 0x85, 0x0a, // Report ID (10) |
| 0x05, 0x0d, // Usage Page (Digitizers) |
| 0x09, 0x20, // Usage (Stylus) |
| 0xa1, 0x00, // Collection (Physical) |
| 0x09, 0x00, // Usage (0x0000) |
| 0x15, 0x00, // Logical Minimum (0) |
| 0x26, 0xff, 0x00, // Logical Maximum (255) |
| 0x75, 0x08, // Report Size (8) |
| 0x95, 0x07, // Report Count (7) |
| 0x81, 0x02, // Input (Data,Var,Abs) |
| 0xc0, // End Collection |
| 0x85, 0x10, // Report ID (16) |
| 0x09, 0x20, // Usage (Stylus) |
| 0xa1, 0x00, // Collection (Physical) |
| 0x09, 0x42, // Usage (Tip Switch) |
| 0x09, 0x44, // Usage (Barrel Switch) |
| 0x09, 0x3c, // Usage (Invert) |
| 0x09, 0x45, // Usage (Eraser) |
| 0x09, 0x32, // Usage (In Range) |
| 0x09, 0x5a, // Usage (Secondary Barrel Switch) <-- added |
| 0x15, 0x00, // Logical Minimum (0) |
| 0x25, 0x01, // Logical Maximum (1) |
| 0x75, 0x01, // Report Size (1) |
| 0x95, 0x06, // Report Count (6) <--- changed from 5 |
| 0x81, 0x02, // Input (Data,Var,Abs) |
| 0x95, 0x02, // Report Count (2) <--- changed from 3 |
| 0x81, 0x03, // Input (Cnst,Var,Abs) |
| 0x05, 0x01, // Usage Page (Generic Desktop) |
| 0x09, 0x30, // Usage (X) |
| 0x75, 0x10, // Report Size (16) |
| 0x95, 0x01, // Report Count (1) |
| 0xa4, // Push |
| 0x55, 0x0d, // Unit Exponent (-3) |
| 0x65, 0x33, // Unit (EnglishLinear: in³) |
| 0x15, 0x00, // Logical Minimum (0) |
| 0x26, 0x00, 0x7d, // Logical Maximum (32000) |
| 0x35, 0x00, // Physical Minimum (0) |
| 0x46, 0x00, 0x7d, // Physical Maximum (32000) |
| 0x81, 0x02, // Input (Data,Var,Abs) |
| 0x09, 0x31, // Usage (Y) |
| 0x15, 0x00, // Logical Minimum (0) |
| 0x26, 0x20, 0x4e, // Logical Maximum (20000) |
| 0x35, 0x00, // Physical Minimum (0) |
| 0x46, 0x20, 0x4e, // Physical Maximum (20000) |
| 0x81, 0x02, // Input (Data,Var,Abs) |
| 0x05, 0x0d, // Usage Page (Digitizers) |
| 0x09, 0x30, // Usage (Tip Pressure) |
| 0x15, 0x00, // Logical Minimum (0) |
| 0x26, 0xff, 0x07, // Logical Maximum (2047) |
| 0x35, 0x00, // Physical Minimum (0) |
| 0x46, 0xff, 0x07, // Physical Maximum (2047) |
| 0x81, 0x02, // Input (Data,Var,Abs) |
| 0x05, 0x0d, // Usage Page (Digitizers) |
| 0x09, 0x3d, // Usage (X Tilt) |
| 0x09, 0x3e, // Usage (Y Tilt) |
| 0x15, 0xc4, // Logical Minimum (-60) <- changed from -127 |
| 0x25, 0x3c, // Logical Maximum (60) <- changed from 127 |
| 0x75, 0x08, // Report Size (8) |
| 0x95, 0x02, // Report Count (2) |
| 0x81, 0x02, // Input (Data,Var,Abs) |
| 0xc0, // End Collection |
| 0xc0, // End Collection |
| 0x05, 0x01, // Usage Page (Generic Desktop) |
| 0x09, 0x06, // Usage (Keyboard) |
| 0xa1, 0x01, // Collection (Application) |
| 0x85, 0x0d, // Report ID (13) |
| 0x05, 0x07, // Usage Page (Keyboard/Keypad) |
| 0x19, 0xe0, // Usage Minimum (224) |
| 0x29, 0xe7, // Usage Maximum (231) |
| 0x15, 0x00, // Logical Minimum (0) |
| 0x25, 0x01, // Logical Maximum (1) |
| 0x75, 0x01, // Report Size (1) |
| 0x95, 0x08, // Report Count (8) |
| 0x81, 0x02, // Input (Data,Var,Abs) |
| 0x75, 0x08, // Report Size (8) |
| 0x95, 0x01, // Report Count (1) |
| 0x81, 0x01, // Input (Cnst,Arr,Abs) |
| 0x05, 0x07, // Usage Page (Keyboard/Keypad) |
| 0x19, 0x00, // Usage Minimum (0) |
| 0x29, 0x65, // Usage Maximum (101) |
| 0x15, 0x00, // Logical Minimum (0) |
| 0x25, 0x65, // Logical Maximum (101) |
| 0x75, 0x08, // Report Size (8) |
| 0x95, 0x05, // Report Count (5) |
| 0x81, 0x00, // Input (Data,Arr,Abs) |
| 0xc0, // End Collection |
| 0x05, 0x0c, // Usage Page (Consumer) |
| 0x09, 0x01, // Usage (Consumer Control) |
| 0xa1, 0x01, // Collection (Application) |
| 0x85, 0x0c, // Report ID (12) |
| 0x09, 0xe9, // Usage (Volume Increment) |
| 0x09, 0xea, // Usage (Volume Decrement) |
| 0x09, 0xe2, // Usage (Mute) |
| 0x15, 0x00, // Logical Minimum (0) |
| 0x25, 0x01, // Logical Maximum (1) |
| 0x75, 0x01, // Report Size (1) |
| 0x95, 0x03, // Report Count (3) |
| 0x81, 0x06, // Input (Data,Var,Rel) |
| 0x75, 0x05, // Report Size (5) |
| 0x95, 0x01, // Report Count (1) |
| 0x81, 0x07, // Input (Cnst,Var,Rel) |
| 0xc0, // End Collection |
| }; |
| |
| static inline unsigned int bitwidth32(__u32 x) |
| { |
| return 32 - __builtin_clzg(x, 32); |
| } |
| |
| static inline unsigned int floor_log2_32(__u32 x) |
| { |
| return bitwidth32(x) - 1; |
| } |
| |
| /* Maps the interval [0, 2047] to itself using a scaled |
| * approximation of the function log2(x+1). |
| */ |
| static unsigned int scaled_log2(__u16 v) |
| { |
| const unsigned int XMAX = 2047; |
| const unsigned int YMAX = 11; /* log2(2048) = 11 */ |
| |
| unsigned int x = v + 1; |
| unsigned int n = floor_log2_32(x); |
| unsigned int b = 1 << n; |
| |
| /* Fixed-point fraction in [0, 1), linearly |
| * interpolated using delta-y = 1 and |
| * delta-x = (2b - b) = b. |
| */ |
| unsigned int frac = (x - b) << YMAX; |
| unsigned int lerp = frac / b; |
| unsigned int log2 = (n << YMAX) + lerp; |
| |
| return ((log2 * XMAX) / YMAX) >> YMAX; |
| } |
| |
| SEC(HID_BPF_RDESC_FIXUP) |
| int BPF_PROG(hid_fix_rdesc, 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); |
| } |
| |
| SEC(HID_BPF_DEVICE_EVENT) |
| int BPF_PROG(waltop_fix_events, struct hid_bpf_ctx *hctx) |
| { |
| __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 10 /* size */); |
| |
| if (!data) |
| return 0; /* EPERM check */ |
| |
| __u8 report_id = data[0]; |
| |
| if (report_id != PEN_REPORT_ID) |
| return 0; |
| |
| /* On this tablet if the secondary barrel switch is pressed, |
| * the tablet sends tip down and barrel down. Change this to |
| * just secondary barrel down when there is no ambiguity. |
| * |
| * It's possible that there is a bug in the firmware and the |
| * device intends to set invert + eraser instead (i.e. the |
| * pysical button is an eraser button) but since |
| * the pressure is always zero, said eraser button |
| * would be useless anyway. |
| * |
| * So let's just change the button to secondary barrel down. |
| */ |
| |
| __u8 tip_switch = data[1] & TIP_SWITCH; |
| __u8 barrel_switch = data[1] & BARREL_SWITCH; |
| |
| __u8 tip_held = last_button_state & TIP_SWITCH; |
| __u8 barrel_held = last_button_state & BARREL_SWITCH; |
| |
| if (tip_switch && barrel_switch && !tip_held && !barrel_held) { |
| data[1] &= ~(TIP_SWITCH | BARREL_SWITCH); /* release tip and barrel */ |
| data[1] |= SECONDARY_BARREL_SWITCH; /* set secondary barrel switch */ |
| } |
| |
| last_button_state = data[1]; |
| |
| /* The pressure sensor on this tablet maps around half of the |
| * logical pressure range into the interval [0-100]. Further |
| * pressure causes the sensor value to increase exponentially |
| * up to a maximum value of 2047. |
| * |
| * The values 12 and 102 were chosen to have an integer slope |
| * with smooth transition between the two curves around the |
| * value 100. |
| */ |
| |
| __u16 pressure = (((__u16)data[6]) << 0) | (((__u16)data[7]) << 8); |
| |
| if (pressure <= 102) |
| pressure *= 12; |
| else |
| pressure = scaled_log2(pressure); |
| |
| data[6] = pressure >> 0; |
| data[7] = pressure >> 8; |
| |
| return 0; |
| } |
| |
| HID_BPF_OPS(waltop_batteryless) = { |
| .hid_device_event = (void *)waltop_fix_events, |
| .hid_rdesc_fixup = (void *)hid_fix_rdesc, |
| }; |
| |
| SEC("syscall") |
| int probe(struct hid_bpf_probe_args *ctx) |
| { |
| if (ctx->rdesc_size == EXPECTED_RDESC_SIZE) |
| ctx->retval = 0; |
| else |
| ctx->retval = -EINVAL; |
| |
| return 0; |
| } |
| |
| char _license[] SEC("license") = "GPL"; |
