new file mode 100644
@@ -0,0 +1,290 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2024 Benjamin Tissoires
+ */
+
+#include "vmlinux.h"
+#include "hid_bpf.h"
+#include "hid_bpf_helpers.h"
+#include <bpf/bpf_tracing.h>
+
+#define VID_HUION 0x256C
+#define PID_KAMVAS_PRO_19 0x006B
+#define NAME_KAMVAS_PRO_19 "HUION Huion Tablet_GT1902"
+
+#define TEST_PREFIX "uhid test "
+
+HID_BPF_CONFIG(
+ HID_DEVICE(BUS_USB, HID_GROUP_MULTITOUCH_WIN_8, VID_HUION, PID_KAMVAS_PRO_19),
+);
+
+bool prev_was_out_of_range;
+bool in_eraser_mode;
+
+/*
+ * We need to amend the report descriptor for the following:
+ * - the second button is reported through Secondary Tip Switch instead of Secondary Barrel Switch
+ * - the third button is reported through Invert, and we need some room to report it.
+ *
+ */
+static const __u8 fixed_rdesc[] = {
+ 0x05, 0x0d, // Usage Page (Digitizers) 0
+ 0x09, 0x02, // Usage (Pen) 2
+ 0xa1, 0x01, // Collection (Application) 4
+ 0x85, 0x0a, // Report ID (10) 6
+ 0x09, 0x20, // Usage (Stylus) 8
+ 0xa1, 0x01, // Collection (Application) 10
+ 0x09, 0x42, // Usage (Tip Switch) 12
+ 0x09, 0x44, // Usage (Barrel Switch) 14
+ 0x09, 0x5a, // Usage (Secondary Barrel Switch) 16 /* changed from Secondary Tip Switch */
+ 0x09, 0x3c, // Usage (Invert) 18
+ 0x09, 0x45, // Usage (Eraser) 20
+ 0x15, 0x00, // Logical Minimum (0) 22
+ 0x25, 0x01, // Logical Maximum (1) 24
+ 0x75, 0x01, // Report Size (1) 26
+ 0x95, 0x05, // Report Count (5) 28 /* changed (was 5) */
+ 0x81, 0x02, // Input (Data,Var,Abs) 30
+ 0x05, 0x09, // Usage Page (Button) /* inserted */
+ 0x09, 0x4a, // Usage (0x4a) /* inserted to be translated as input usage 0x149: BTN_STYLUS3 */
+ 0x95, 0x01, // Report Count (1) /* inserted */
+ 0x81, 0x02, // Input (Data,Var,Abs) /* inserted */
+ 0x05, 0x0d, // Usage Page (Digitizers) /* inserted */
+ 0x09, 0x32, // Usage (In Range) 32
+ 0x75, 0x01, // Report Size (1) 34
+ 0x95, 0x01, // Report Count (1) 36
+ 0x81, 0x02, // Input (Data,Var,Abs) 38
+ 0x81, 0x03, // Input (Cnst,Var,Abs) 40
+ 0x05, 0x01, // Usage Page (Generic Desktop) 42
+ 0x09, 0x30, // Usage (X) 44
+ 0x09, 0x31, // Usage (Y) 46
+ 0x55, 0x0d, // Unit Exponent (-3) 48
+ 0x65, 0x33, // Unit (EnglishLinear: in³) 50
+ 0x26, 0xff, 0x7f, // Logical Maximum (32767) 52
+ 0x35, 0x00, // Physical Minimum (0) 55
+ 0x46, 0x00, 0x08, // Physical Maximum (2048) 57
+ 0x75, 0x10, // Report Size (16) 60
+ 0x95, 0x02, // Report Count (2) 62
+ 0x81, 0x02, // Input (Data,Var,Abs) 64
+ 0x05, 0x0d, // Usage Page (Digitizers) 66
+ 0x09, 0x30, // Usage (Tip Pressure) 68
+ 0x26, 0xff, 0x3f, // Logical Maximum (16383) 70
+ 0x75, 0x10, // Report Size (16) 73
+ 0x95, 0x01, // Report Count (1) 75
+ 0x81, 0x02, // Input (Data,Var,Abs) 77
+ 0x09, 0x3d, // Usage (X Tilt) 79
+ 0x09, 0x3e, // Usage (Y Tilt) 81
+ 0x15, 0xa6, // Logical Minimum (-90) 83
+ 0x25, 0x5a, // Logical Maximum (90) 85
+ 0x75, 0x08, // Report Size (8) 87
+ 0x95, 0x02, // Report Count (2) 89
+ 0x81, 0x02, // Input (Data,Var,Abs) 91
+ 0xc0, // End Collection 93
+ 0xc0, // End Collection 94
+ 0x05, 0x0d, // Usage Page (Digitizers) 95
+ 0x09, 0x04, // Usage (Touch Screen) 97
+ 0xa1, 0x01, // Collection (Application) 99
+ 0x85, 0x04, // Report ID (4) 101
+ 0x09, 0x22, // Usage (Finger) 103
+ 0xa1, 0x02, // Collection (Logical) 105
+ 0x05, 0x0d, // Usage Page (Digitizers) 107
+ 0x95, 0x01, // Report Count (1) 109
+ 0x75, 0x06, // Report Size (6) 111
+ 0x09, 0x51, // Usage (Contact Id) 113
+ 0x15, 0x00, // Logical Minimum (0) 115
+ 0x25, 0x3f, // Logical Maximum (63) 117
+ 0x81, 0x02, // Input (Data,Var,Abs) 119
+ 0x09, 0x42, // Usage (Tip Switch) 121
+ 0x25, 0x01, // Logical Maximum (1) 123
+ 0x75, 0x01, // Report Size (1) 125
+ 0x95, 0x01, // Report Count (1) 127
+ 0x81, 0x02, // Input (Data,Var,Abs) 129
+ 0x75, 0x01, // Report Size (1) 131
+ 0x95, 0x01, // Report Count (1) 133
+ 0x81, 0x03, // Input (Cnst,Var,Abs) 135
+ 0x05, 0x01, // Usage Page (Generic Desktop) 137
+ 0x75, 0x10, // Report Size (16) 139
+ 0x55, 0x0e, // Unit Exponent (-2) 141
+ 0x65, 0x11, // Unit (SILinear: cm) 143
+ 0x09, 0x30, // Usage (X) 145
+ 0x26, 0xff, 0x7f, // Logical Maximum (32767) 147
+ 0x35, 0x00, // Physical Minimum (0) 150
+ 0x46, 0x15, 0x0c, // Physical Maximum (3093) 152
+ 0x81, 0x42, // Input (Data,Var,Abs,Null) 155
+ 0x09, 0x31, // Usage (Y) 157
+ 0x26, 0xff, 0x7f, // Logical Maximum (32767) 159
+ 0x46, 0xcb, 0x06, // Physical Maximum (1739) 162
+ 0x81, 0x42, // Input (Data,Var,Abs,Null) 165
+ 0x05, 0x0d, // Usage Page (Digitizers) 167
+ 0x09, 0x30, // Usage (Tip Pressure) 169
+ 0x26, 0xff, 0x1f, // Logical Maximum (8191) 171
+ 0x75, 0x10, // Report Size (16) 174
+ 0x95, 0x01, // Report Count (1) 176
+ 0x81, 0x02, // Input (Data,Var,Abs) 178
+ 0xc0, // End Collection 180
+ 0x05, 0x0d, // Usage Page (Digitizers) 181
+ 0x09, 0x22, // Usage (Finger) 183
+ 0xa1, 0x02, // Collection (Logical) 185
+ 0x05, 0x0d, // Usage Page (Digitizers) 187
+ 0x95, 0x01, // Report Count (1) 189
+ 0x75, 0x06, // Report Size (6) 191
+ 0x09, 0x51, // Usage (Contact Id) 193
+ 0x15, 0x00, // Logical Minimum (0) 195
+ 0x25, 0x3f, // Logical Maximum (63) 197
+ 0x81, 0x02, // Input (Data,Var,Abs) 199
+ 0x09, 0x42, // Usage (Tip Switch) 201
+ 0x25, 0x01, // Logical Maximum (1) 203
+ 0x75, 0x01, // Report Size (1) 205
+ 0x95, 0x01, // Report Count (1) 207
+ 0x81, 0x02, // Input (Data,Var,Abs) 209
+ 0x75, 0x01, // Report Size (1) 211
+ 0x95, 0x01, // Report Count (1) 213
+ 0x81, 0x03, // Input (Cnst,Var,Abs) 215
+ 0x05, 0x01, // Usage Page (Generic Desktop) 217
+ 0x75, 0x10, // Report Size (16) 219
+ 0x55, 0x0e, // Unit Exponent (-2) 221
+ 0x65, 0x11, // Unit (SILinear: cm) 223
+ 0x09, 0x30, // Usage (X) 225
+ 0x26, 0xff, 0x7f, // Logical Maximum (32767) 227
+ 0x35, 0x00, // Physical Minimum (0) 230
+ 0x46, 0x15, 0x0c, // Physical Maximum (3093) 232
+ 0x81, 0x42, // Input (Data,Var,Abs,Null) 235
+ 0x09, 0x31, // Usage (Y) 237
+ 0x26, 0xff, 0x7f, // Logical Maximum (32767) 239
+ 0x46, 0xcb, 0x06, // Physical Maximum (1739) 242
+ 0x81, 0x42, // Input (Data,Var,Abs,Null) 245
+ 0x05, 0x0d, // Usage Page (Digitizers) 247
+ 0x09, 0x30, // Usage (Tip Pressure) 249
+ 0x26, 0xff, 0x1f, // Logical Maximum (8191) 251
+ 0x75, 0x10, // Report Size (16) 254
+ 0x95, 0x01, // Report Count (1) 256
+ 0x81, 0x02, // Input (Data,Var,Abs) 258
+ 0xc0, // End Collection 260
+ 0x05, 0x0d, // Usage Page (Digitizers) 261
+ 0x09, 0x56, // Usage (Scan Time) 263
+ 0x55, 0x00, // Unit Exponent (0) 265
+ 0x65, 0x00, // Unit (None) 267
+ 0x27, 0xff, 0xff, 0xff, 0x7f, // Logical Maximum (2147483647) 269
+ 0x95, 0x01, // Report Count (1) 274
+ 0x75, 0x20, // Report Size (32) 276
+ 0x81, 0x02, // Input (Data,Var,Abs) 278
+ 0x09, 0x54, // Usage (Contact Count) 280
+ 0x25, 0x7f, // Logical Maximum (127) 282
+ 0x95, 0x01, // Report Count (1) 284
+ 0x75, 0x08, // Report Size (8) 286
+ 0x81, 0x02, // Input (Data,Var,Abs) 288
+ 0x75, 0x08, // Report Size (8) 290
+ 0x95, 0x08, // Report Count (8) 292
+ 0x81, 0x03, // Input (Cnst,Var,Abs) 294
+ 0x85, 0x05, // Report ID (5) 296
+ 0x09, 0x55, // Usage (Contact Max) 298
+ 0x25, 0x0a, // Logical Maximum (10) 300
+ 0x75, 0x08, // Report Size (8) 302
+ 0x95, 0x01, // Report Count (1) 304
+ 0xb1, 0x02, // Feature (Data,Var,Abs) 306
+ 0x06, 0x00, 0xff, // Usage Page (Vendor Defined Page 1) 308
+ 0x09, 0xc5, // Usage (Vendor Usage 0xc5) 311
+ 0x85, 0x06, // Report ID (6) 313
+ 0x15, 0x00, // Logical Minimum (0) 315
+ 0x26, 0xff, 0x00, // Logical Maximum (255) 317
+ 0x75, 0x08, // Report Size (8) 320
+ 0x96, 0x00, 0x01, // Report Count (256) 322
+ 0xb1, 0x02, // Feature (Data,Var,Abs) 325
+ 0xc0, // End Collection 327
+};
+
+SEC("fmod_ret/hid_bpf_rdesc_fixup")
+int BPF_PROG(hid_fix_rdesc_huion_kamvas_pro_19, struct hid_bpf_ctx *hctx)
+{
+ __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, HID_MAX_DESCRIPTOR_SIZE /* size */);
+
+ if (!data)
+ return 0; /* EPERM check */
+
+ __builtin_memcpy(data, fixed_rdesc, sizeof(fixed_rdesc));
+
+ return sizeof(fixed_rdesc);
+}
+
+/*
+ * This tablet reports the 3rd button through invert, but this conflict
+ * with the normal eraser mode.
+ * Fortunately, before entering eraser mode, (so Invert = 1),
+ * the tablet always sends an out-of-proximity event.
+ * So we can detect that single event and:
+ * - if there was none but the invert bit was toggled: this is the
+ * third button
+ * - if there was this out-of-proximity event, we are entering
+ * eraser mode, and we will until the next out-of-proximity.
+ */
+SEC("fmod_ret/hid_bpf_device_event")
+int BPF_PROG(kamvas_pro_19_fix_3rd_button, struct hid_bpf_ctx *hctx)
+{
+ __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 10 /* size */);
+
+ if (!data)
+ return 0; /* EPERM check */
+
+ if (data[0] != 0x0a) /* not the pen report ID */
+ return 0;
+
+ /* stylus is out of range */
+ if (!(data[1] & 0x40)) {
+ prev_was_out_of_range = true;
+ in_eraser_mode = false;
+ return 0;
+ }
+
+ /* going into eraser mode (Invert = 1) only happens after an
+ * out of range event
+ */
+ if (prev_was_out_of_range && (data[1] & 0x18))
+ in_eraser_mode = true;
+
+ /* eraser mode works fine */
+ if (in_eraser_mode)
+ return 0;
+
+ /* copy the Invert bit reported for the 3rd button in bit 7 */
+ if (data[1] & 0x08)
+ data[1] |= 0x20;
+
+ /* clear Invert bit now that it was copied */
+ data[1] &= 0xf7;
+
+ prev_was_out_of_range = false;
+
+ return 0;
+}
+
+SEC("syscall")
+int probe(struct hid_bpf_probe_args *ctx)
+{
+ ctx->retval = ctx->rdesc_size != 328;
+ if (ctx->retval)
+ ctx->retval = -EINVAL;
+
+ /* ensure the kernel isn't fixed already */
+ if (ctx->rdesc[17] != 0x43) /* Secondary Tip Switch */
+ ctx->retval = -EINVAL;
+
+ struct hid_bpf_ctx *hctx = hid_bpf_allocate_context(ctx->hid);
+
+ if (!hctx) {
+ return ctx->retval = -EINVAL;
+ return 0;
+ }
+
+ const char *name = hctx->hid->name;
+
+ /* strip out TEST_PREFIX */
+ if (!__builtin_memcmp(name, TEST_PREFIX, sizeof(TEST_PREFIX) - 1))
+ name += sizeof(TEST_PREFIX) - 1;
+
+ if (__builtin_memcmp(name, NAME_KAMVAS_PRO_19, sizeof(NAME_KAMVAS_PRO_19)))
+ ctx->retval = -EINVAL;
+
+ hid_bpf_release_context(hctx);
+
+ return 0;
+}
+
+char _license[] SEC("license") = "GPL";
This tablets gets a lot of things wrong: - the secondary button is reported through Secondary Tip Switch - the third button is reported through Invert Fortunately, before entering eraser mode, (so Invert = 1), the tablet always sends an out-of-proximity event. So we can detect that single event and: - if there was none but the invert bit was toggled: this is the third button - if there was this out-of-proximity event, we are entering eraser mode, and we will until the next out-of-proximity. Signed-off-by: Benjamin Tissoires <bentiss@kernel.org> --- drivers/hid/bpf/progs/Huion__Kamvas-Pro-19.bpf.c | 290 +++++++++++++++++++++++ 1 file changed, 290 insertions(+)