[PATCH 7/8] HID: bpf: Add support for the Huion KeyDial K20 over bluetooth
From: Benjamin Tissoires
Date: Fri Apr 03 2026 - 12:25:33 EST
When connected over bluetooth this device is just different enough that
forcing it into the same source file as the USB connection doesn't gain
us much benefit. So let's duplicate this.
Code and tests originally produced by Claude code.
Link: https://gitlab.freedesktop.org/libevdev/udev-hid-bpf/-/work_items/69
Link: https://gitlab.freedesktop.org/libevdev/udev-hid-bpf/-/merge_requests/201
Signed-off-by: Peter Hutterer <peter.hutterer@xxxxxxxxx>
Signed-off-by: Benjamin Tissoires <bentiss@xxxxxxxxxx>
---
.../bpf/progs/Huion__KeydialK20-Bluetooth.bpf.c | 492 +++++++++++++++++++++
1 file changed, 492 insertions(+)
diff --git a/drivers/hid/bpf/progs/Huion__KeydialK20-Bluetooth.bpf.c b/drivers/hid/bpf/progs/Huion__KeydialK20-Bluetooth.bpf.c
new file mode 100644
index 000000000000..d0769e990039
--- /dev/null
+++ b/drivers/hid/bpf/progs/Huion__KeydialK20-Bluetooth.bpf.c
@@ -0,0 +1,492 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2024 Red Hat, Inc
+ */
+
+#include "vmlinux.h"
+#include "hid_bpf.h"
+#include "hid_bpf_helpers.h"
+#include "hid_report_helpers.h"
+#include <bpf/bpf_tracing.h>
+
+#define VID_HUION 0x256C
+#define PID_KEYDIAL_K20_BLUETOOTH 0x8251
+
+HID_BPF_CONFIG(
+ HID_DEVICE(BUS_BLUETOOTH, HID_GROUP_GENERIC, VID_HUION, PID_KEYDIAL_K20_BLUETOOTH),
+);
+
+/* This is the same device as in 0010-Huion__KeydialK20 but connected via Bluetooth.
+ * It does not need (to support?) switching to a vendor mode so we just modify the
+ * existing mode.
+ *
+ * By default it exports two hidraw nodes, only the second one sends events.
+ *
+ * This is the first hidraw node which we disable:
+ *
+ * # Keydial mini-050
+ * # Report descriptor length: 114 bytes
+ * # Bytes // Field Name Offset
+ * # ----------------------------------------------------------------------------------
+ * # 🮥 0x05, 0x01, // Usage Page (Generic Desktop) 0
+ * # 🭬 0x09, 0x0e, // Usage (System Multi-Axis Controller) 2
+ * # 0xa1, 0x01, // Collection (Application) 4
+ * # ┅ 0x85, 0x03, // Report ID (3) 6
+ * # 🮥 0x05, 0x0d, // Usage Page (Digitizers) 8
+ * # 0x75, 0x08, // Report Size (8) 10
+ * # 0x95, 0x01, // Report Count (1) 12
+ * # ┇ 0x81, 0x01, // Input (Cnst,Arr,Abs) 14
+ * # 🭬 0x09, 0x21, // Usage (Puck) 16
+ * # 0xa1, 0x02, // Collection (Logical) 18
+ * # 0x15, 0x00, // Logical Minimum (0) 20
+ * # 0x25, 0x01, // Logical Maximum (1) 22
+ * # 0x75, 0x01, // Report Size (1) 24
+ * # 0x95, 0x01, // Report Count (1) 26
+ * # 0xa1, 0x00, // Collection (Physical) 28
+ * # 🮥 0x05, 0x09, // Usage Page (Button) 30
+ * # 🭬 0x09, 0x01, // Usage (Button 1) 32
+ * # ┇ 0x81, 0x02, // Input (Data,Var,Abs) 34
+ * # 🮥 0x05, 0x0d, // Usage Page (Digitizers) 36
+ * # 🭬 0x09, 0x33, // Usage (Touch) 38
+ * # ┇ 0x81, 0x02, // Input (Data,Var,Abs) 40
+ * # 0x95, 0x06, // Report Count (6) 42
+ * # ┇ 0x81, 0x03, // Input (Cnst,Var,Abs) 44
+ * # 0xa1, 0x02, // Collection (Logical) 46
+ * # 🮥 0x05, 0x01, // Usage Page (Generic Desktop) 48
+ * # 🭬 0x09, 0x37, // Usage (Dial) 50
+ * # 0x16, 0x00, 0x80, // Logical Minimum (32768) 52
+ * # 0x26, 0xff, 0x7f, // Logical Maximum (32767) 55
+ * # 0x75, 0x10, // Report Size (16) 58
+ * # 0x95, 0x01, // Report Count (1) 60
+ * # ┇ 0x81, 0x06, // Input (Data,Var,Rel) 62
+ * # 0x35, 0x00, // Physical Minimum (0) 64
+ * # 0x46, 0x10, 0x0e, // Physical Maximum (3600) 66
+ * # 0x15, 0x00, // Logical Minimum (0) 69
+ * # 0x26, 0x10, 0x0e, // Logical Maximum (3600) 71
+ * # 🭬 0x09, 0x48, // Usage (Resolution Multiplier) 74
+ * # ║ 0xb1, 0x02, // Feature (Data,Var,Abs) 76
+ * # 0x45, 0x00, // Physical Maximum (0) 78
+ * # 0xc0, // End Collection 80
+ * # 0x75, 0x08, // Report Size (8) 81
+ * # 0x95, 0x01, // Report Count (1) 83
+ * # ┇ 0x81, 0x01, // Input (Cnst,Arr,Abs) 85
+ * # 0x75, 0x08, // Report Size (8) 87
+ * # 0x95, 0x01, // Report Count (1) 89
+ * # ┇ 0x81, 0x01, // Input (Cnst,Arr,Abs) 91
+ * # 0x75, 0x08, // Report Size (8) 93
+ * # 0x95, 0x01, // Report Count (1) 95
+ * # ┇ 0x81, 0x01, // Input (Cnst,Arr,Abs) 97
+ * # 0x75, 0x08, // Report Size (8) 99
+ * # 0x95, 0x01, // Report Count (1) 101
+ * # ┇ 0x81, 0x01, // Input (Cnst,Arr,Abs) 103
+ * # 0x75, 0x08, // Report Size (8) 105
+ * # 0x95, 0x01, // Report Count (1) 107
+ * # ┇ 0x81, 0x01, // Input (Cnst,Arr,Abs) 109
+ * # 0xc0, // End Collection 111
+ * # 0xc0, // End Collection 112
+ * # 0xc0, // End Collection 113
+ * R: 114 05 01 09 0e a1 01 85 03 05 0d 75 08 95 01 81 01 09 21 a1 02 15 00 25 01 75 01 95 01 a1 00 05 09 09 01 81 02 05 0d 09 33 81 02 95 06 81 03 a1 02 05 01 09 37 16 00 80 26 ff 7f 75 10 95 01 81 06 35 00 46 10 0e 15 00 26 10 0e 09 48 b1 02 45 00 c0 75 08 95 01 81 01 75 08 95 01 81 01 75 08 95 01 81 01 75 08 95 01 81 01 75 08 95 01 81 01 c0 c0 c0
+ * N: Keydial mini-050
+ * I: 5 256c 8251
+ *
+ * The second hidraw node is what sends events:
+ *
+ * # Keydial mini-050
+ * # Report descriptor length: 160 bytes
+ * # Bytes // Field Name Offset
+ * # ----------------------------------------------------------------------------------
+ * # 🮥 0x05, 0x01, // Usage Page (Generic Desktop) 0
+ * # 🭬 0x09, 0x06, // Usage (Keyboard) 2
+ * # 0xa1, 0x01, // Collection (Application) 4
+ * # ┅ 0x85, 0x01, // Report ID (1) 6
+ * # 🮥 0x05, 0x07, // Usage Page (Keyboard/Keypad) 8
+ * # 🭬 0x19, 0xe0, // Usage Minimum (224) 10
+ * # 🭬 0x29, 0xe7, // Usage Maximum (231) 12
+ * # 0x15, 0x00, // Logical Minimum (0) 14
+ * # 0x25, 0x01, // Logical Maximum (1) 16
+ * # 0x75, 0x01, // Report Size (1) 18
+ * # 0x95, 0x08, // Report Count (8) 20
+ * # ┇ 0x81, 0x02, // Input (Data,Var,Abs) 22
+ * # 0x95, 0x01, // Report Count (1) 24
+ * # 0x75, 0x08, // Report Size (8) 26
+ * # ┇ 0x81, 0x01, // Input (Cnst,Arr,Abs) 28
+ * # 0x95, 0x05, // Report Count (5) 30
+ * # 0x75, 0x01, // Report Size (1) 32
+ * # 🮥 0x05, 0x08, // Usage Page (LED) 34
+ * # 🭬 0x19, 0x01, // Usage Minimum (1) 36
+ * # 🭬 0x29, 0x05, // Usage Maximum (5) 38
+ * # ┊ 0x91, 0x02, // Output (Data,Var,Abs) 40
+ * # 0x95, 0x01, // Report Count (1) 42
+ * # 0x75, 0x03, // Report Size (3) 44
+ * # ┊ 0x91, 0x01, // Output (Cnst,Arr,Abs) 46
+ * # 0x95, 0x06, // Report Count (6) 48
+ * # 0x75, 0x08, // Report Size (8) 50
+ * # 0x15, 0x00, // Logical Minimum (0) 52
+ * # 0x25, 0xf1, // Logical Maximum (241) 54
+ * # 🮥 0x05, 0x07, // Usage Page (Keyboard/Keypad) 56
+ * # 🭬 0x19, 0x00, // Usage Minimum (0) 58
+ * # 🭬 0x29, 0xf1, // Usage Maximum (241) 60
+ * # ┇ 0x81, 0x00, // Input (Data,Arr,Abs) 62
+ * # 0xc0, // End Collection 64
+ * # 🮥 0x05, 0x0c, // Usage Page (Consumer) 65
+ * # 🭬 0x09, 0x01, // Usage (Consumer Control) 67
+ * # 0xa1, 0x01, // Collection (Application) 69
+ * # ┅ 0x85, 0x02, // Report ID (2) 71
+ * # 🮥 0x05, 0x0c, // Usage Page (Consumer) 73
+ * # 🭬 0x19, 0x00, // Usage Minimum (0) 75
+ * # 🭬 0x2a, 0x80, 0x03, // Usage Maximum (896) 77
+ * # 0x15, 0x00, // Logical Minimum (0) 80
+ * # 0x26, 0x80, 0x03, // Logical Maximum (896) 82
+ * # 0x75, 0x10, // Report Size (16) 85
+ * # 0x95, 0x01, // Report Count (1) 87
+ * # ┇ 0x81, 0x00, // Input (Data,Arr,Abs) 89
+ * # 0xc0, // End Collection 91
+ * # 🮥 0x05, 0x01, // Usage Page (Generic Desktop) 92
+ * # 🭬 0x09, 0x02, // Usage (Mouse) 94
+ * # 0xa1, 0x01, // Collection (Application) 96
+ * # 🭬 0x09, 0x01, // Usage (Pointer) 98
+ * # ┅ 0x85, 0x05, // Report ID (5) 100
+ * # 0xa1, 0x00, // Collection (Physical) 102
+ * # 🮥 0x05, 0x09, // Usage Page (Button) 104
+ * # 🭬 0x19, 0x01, // Usage Minimum (1) 106
+ * # 🭬 0x29, 0x05, // Usage Maximum (5) 108
+ * # 0x15, 0x00, // Logical Minimum (0) 110
+ * # 0x25, 0x01, // Logical Maximum (1) 112
+ * # 0x95, 0x05, // Report Count (5) 114
+ * # 0x75, 0x01, // Report Size (1) 116
+ * # ┇ 0x81, 0x02, // Input (Data,Var,Abs) 118
+ * # 0x95, 0x01, // Report Count (1) 120
+ * # 0x75, 0x03, // Report Size (3) 122
+ * # ┇ 0x81, 0x01, // Input (Cnst,Arr,Abs) 124
+ * # 🮥 0x05, 0x01, // Usage Page (Generic Desktop) 126
+ * # 🭬 0x09, 0x30, // Usage (X) 128
+ * # 🭬 0x09, 0x31, // Usage (Y) 130
+ * # 0x16, 0x01, 0x80, // Logical Minimum (32769) 132
+ * # 0x26, 0xff, 0x7f, // Logical Maximum (32767) 135
+ * # 0x75, 0x10, // Report Size (16) 138
+ * # 0x95, 0x02, // Report Count (2) 140
+ * # ┇ 0x81, 0x06, // Input (Data,Var,Rel) 142
+ * # 🮥 0x05, 0x01, // Usage Page (Generic Desktop) 144
+ * # 🭬 0x09, 0x38, // Usage (Wheel) 146
+ * # 0x15, 0x81, // Logical Minimum (129) 148
+ * # 0x25, 0x7f, // Logical Maximum (127) 150
+ * # 0x95, 0x01, // Report Count (1) 152
+ * # 0x75, 0x08, // Report Size (8) 154
+ * # ┇ 0x81, 0x06, // Input (Data,Var,Rel) 156
+ * # 0xc0, // End Collection 158
+ * # 0xc0, // End Collection 159
+ * R: 160 05 01 09 06 a1 01 85 01 05 07 19 e0 29 e7 15 00 25 01 75 01 95 08 81 02 95 01 75 08 81 01 95 05 75 01 05 08 19 01 29 05 91 02 95 01 75 03 91 01 95 06 75 08 15 00 25 f1 05 07 19 00 29 f1 81 00 c0 05 0c 09 01 a1 01 85 02 05 0c 19 00 2a 80 03 15 00 26 80 03 75 10 95 01 81 00 c0 05 01 09 02 a1 01 09 01 85 05 a1 00 05 09 19 01 29 05 15 00 25 01 95 05 75 01 81 02 95 01 75 03 81 01 05 01 09 30 09 31 16 01 80 26 ff 7f 75 10 95 02 81 06 05 01 09 38 15 81 25 7f 95 01 75 08 81 06 c0 c0
+ * N: Keydial mini-050
+ * I: 5 256c 8251
+ * # Report descriptor:
+ * # ------- Input Report -------
+ * # ░ Report ID: 1
+ * # ░ | Report size: 72 bits
+ * # ░ Bit: 8 Usage: 0007/00e0: Keyboard/Keypad / Keyboard LeftControl Logical Range: 0..=1
+ * # ░ Bit: 9 Usage: 0007/00e1: Keyboard/Keypad / Keyboard LeftShift Logical Range: 0..=1
+ * # ░ Bit: 10 Usage: 0007/00e2: Keyboard/Keypad / Keyboard LeftAlt Logical Range: 0..=1
+ * # ░ Bit: 11 Usage: 0007/00e3: Keyboard/Keypad / Keyboard Left GUI Logical Range: 0..=1
+ * # ░ Bit: 12 Usage: 0007/00e4: Keyboard/Keypad / Keyboard RightControl Logical Range: 0..=1
+ * # ░ Bit: 13 Usage: 0007/00e5: Keyboard/Keypad / Keyboard RightShift Logical Range: 0..=1
+ * # ░ Bit: 14 Usage: 0007/00e6: Keyboard/Keypad / Keyboard RightAlt Logical Range: 0..=1
+ * # ░ Bit: 15 Usage: 0007/00e7: Keyboard/Keypad / Keyboard Right GUI Logical Range: 0..=1
+ * # ░ Bits: 16..=23 ######### Padding
+ * # ░ Bits: 24..=71 Usages: Logical Range: 0..=241
+ * # ░ 0007/0000: <unknown>
+ * # ░ 0007/0001: Keyboard/Keypad / ErrorRollOver
+ * # ░ 0007/0002: Keyboard/Keypad / POSTFail
+ * # ░ 0007/0003: Keyboard/Keypad / ErrorUndefined
+ * # ░ 0007/0004: Keyboard/Keypad / Keyboard A
+ * # ░ ... use --full to see all usages
+ * # ------- Input Report -------
+ * # ▒ Report ID: 2
+ * # ▒ | Report size: 24 bits
+ * # ▒ Bits: 8..=23 Usages: Logical Range: 0..=896
+ * # ▒ 000c/0000: <unknown>
+ * # ▒ 000c/0001: Consumer / Consumer Control
+ * # ▒ 000c/0002: Consumer / Numeric Key Pad
+ * # ▒ 000c/0003: Consumer / Programmable Buttons
+ * # ▒ 000c/0004: Consumer / Microphone
+ * # ▒ ... use --full to see all usages
+ * # ------- Input Report -------
+ * # ▞ Report ID: 5
+ * # ▞ | Report size: 56 bits
+ * # ▞ Bit: 8 Usage: 0009/0001: Button / Button 1 Logical Range: 0..=1
+ * # ▞ Bit: 9 Usage: 0009/0002: Button / Button 2 Logical Range: 0..=1
+ * # ▞ Bit: 10 Usage: 0009/0003: Button / Button 3 Logical Range: 0..=1
+ * # ▞ Bit: 11 Usage: 0009/0004: Button / Button 4 Logical Range: 0..=1
+ * # ▞ Bit: 12 Usage: 0009/0005: Button / Button 5 Logical Range: 0..=1
+ * # ▞ Bits: 13..=15 ######### Padding
+ * # ▞ Bits: 16..=31 Usage: 0001/0030: Generic Desktop / X Logical Range: 32769..=32767
+ * # ▞ Bits: 32..=47 Usage: 0001/0031: Generic Desktop / Y Logical Range: 32769..=32767
+ * # ▞ Bits: 48..=55 Usage: 0001/0038: Generic Desktop / Wheel Logical Range: 129..=127
+ * # ------- Output Report -------
+ * # ░ Report ID: 1
+ * # ░ | Report size: 16 bits
+ * # ░ Bit: 8 Usage: 0008/0001: LED / Num Lock Logical Range: 0..=1
+ * # ░ Bit: 9 Usage: 0008/0002: LED / Caps Lock Logical Range: 0..=1
+ * # ░ Bit: 10 Usage: 0008/0003: LED / Scroll Lock Logical Range: 0..=1
+ * # ░ Bit: 11 Usage: 0008/0004: LED / Compose Logical Range: 0..=1
+ * # ░ Bit: 12 Usage: 0008/0005: LED / Kana Logical Range: 0..=1
+ * # ░ Bits: 13..=15 ######### Padding
+ * ##############################################################################
+ * # Event nodes:
+ * # - /dev/input/event12: "Keydial mini-050 Keyboard"
+ * # - /dev/input/event14: "Keydial mini-050 Mouse"
+ * ##############################################################################
+ * # Recorded events below in format:
+ * # E: <seconds>.<microseconds> <length-in-bytes> [bytes ...]
+ * #
+ *
+ * - Report ID 1 sends keyboard shortcuts when pressing the buttons, e.g.
+ *
+ * # ░ Report ID: 1 /
+ * # ░ Keyboard LeftControl: 0 |Keyboard LeftShift: 0 |Keyboard LeftAlt: 0 |Keyboard Left GUI: 0 |Keyboard RightControl: 0 |Keyboard RightShift: 0 |Keyboard RightAlt: 0 |Keyboard Right GUI: 0 |<8 bits padding> |0007/0000: 0| Keyboard K: 14| 0007/0000: 0| 0007/0000: 0| 0007/0000: 0| 0007/0000: 0
+ * E: 000000.000292 9 01 00 00 00 0e 00 00 00 00
+ *
+ * - Report ID 2 sends the button inside the wheel/dial thing
+ * # ▒ Report ID: 2 /
+ * # ▒ Play/Pause: 205
+ * E: 000134.347845 3 02 cd 00
+ * # ▒ Report ID: 2 /
+ * # ▒ 000c/0000: 0
+ * E: 000134.444965 3 02 00 00
+ *
+ * - Report ID 5 sends the wheel relative events (always a double-event with the second as zero)
+ * # ▞ Report ID: 5 /
+ * # ▞ Button 1: 0 |Button 2: 0 |Button 3: 0 |Button 4: 0 |Button 5: 0 |<3 bits padding> |X: 0 |Y: 0 |Wheel: 255
+ * E: 000064.859915 7 05 00 00 00 00 00 ff
+ * # ▞ Report ID: 5 /
+ * # ▞ Button 1: 0 |Button 2: 0 |Button 3: 0 |Button 4: 0 |Button 5: 0 |<3 bits padding> |X: 0 |Y: 0 |Wheel: 0
+ * E: 000064.882009 7 05 00 00 00 00 00 00
+ */
+
+#define BT_PAD_REPORT_DESCRIPTOR_LENGTH 160
+#define BT_PUCK_REPORT_DESCRIPTOR_LENGTH 114 // This one doesn't send events
+#define BT_PAD_KBD_REPORT_ID 1
+#define BT_PAD_CC_REPORT_ID 2
+#define BT_PAD_MOUSE_REPORT_ID 5
+#define BT_PAD_KBD_REPORT_LENGTH 9
+#define BT_PAD_CC_REPORT_LENGTH 3
+#define BT_PAD_MOUSE_REPORT_LENGTH 7
+#define OUR_REPORT_ID 11 /* "randomly" picked report ID for our reports */
+
+__u32 last_button_state = 0;
+
+static const __u8 disabled_rdesc_puck[] = {
+ FixedSizeVendorReport(BT_PUCK_REPORT_DESCRIPTOR_LENGTH)
+};
+
+static const __u8 fixed_rdesc_pad[] = {
+ UsagePage_GenericDesktop
+ Usage_GD_Keypad
+ CollectionApplication(
+ // Byte 0
+ ReportId(OUR_REPORT_ID)
+ UsagePage_Digitizers
+ Usage_Dig_TabletFunctionKeys
+ CollectionPhysical(
+ // Byte 1 is a button so we look like a tablet
+ Usage_Dig_BarrelSwitch // BTN_STYLUS, needed so we get to be a tablet pad
+ ReportCount(1)
+ ReportSize(1)
+ Input(Var|Abs)
+ ReportCount(7) // Padding
+ Input(Const)
+ // Bytes 2/3 - x/y just exist so we get to be a tablet pad
+ UsagePage_GenericDesktop
+ Usage_GD_X
+ Usage_GD_Y
+ LogicalMinimum_i8(0x0)
+ LogicalMaximum_i8(0x1)
+ ReportCount(2)
+ ReportSize(8)
+ Input(Var|Abs)
+ // Bytes 4-7 are the button state for 19 buttons + pad out to u32
+ // We send the first 10 buttons as buttons 1-10 which is BTN_0 -> BTN_9
+ UsagePage_Button
+ UsageMinimum_i8(1)
+ UsageMaximum_i8(10)
+ LogicalMinimum_i8(0x0)
+ LogicalMaximum_i8(0x1)
+ ReportCount(10)
+ ReportSize(1)
+ Input(Var|Abs)
+ // We send the other 9 buttons as buttons 0x31 and above -> BTN_A - BTN_TL2
+ UsageMinimum_i8(0x31)
+ UsageMaximum_i8(0x3a)
+ ReportCount(9)
+ ReportSize(1)
+ Input(Var|Abs)
+ ReportCount(13)
+ ReportSize(1)
+ Input(Const) // padding
+ // Byte 8 is the wheel
+ UsagePage_GenericDesktop
+ Usage_GD_Wheel
+ LogicalMinimum_i8(-1)
+ LogicalMaximum_i8(1)
+ ReportCount(1)
+ ReportSize(8)
+ Input(Var|Rel)
+ )
+ // Make sure we match our original report length
+ FixedSizeVendorReport(BT_PAD_KBD_REPORT_LENGTH)
+ )
+};
+
+SEC(HID_BPF_RDESC_FIXUP)
+int BPF_PROG(k20_bt_fix_rdesc, struct hid_bpf_ctx *hctx)
+{
+ __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, HID_MAX_DESCRIPTOR_SIZE /* size */);
+ __s32 rdesc_size = hctx->size;
+
+ if (!data)
+ return 0; /* EPERM check */
+
+ if (rdesc_size == BT_PAD_REPORT_DESCRIPTOR_LENGTH) {
+ __builtin_memcpy(data, fixed_rdesc_pad, sizeof(fixed_rdesc_pad));
+ return sizeof(fixed_rdesc_pad);
+ }
+ if (rdesc_size == BT_PUCK_REPORT_DESCRIPTOR_LENGTH) {
+ // This hidraw node doesn't send anything and can be ignored
+ __builtin_memcpy(data, disabled_rdesc_puck, sizeof(disabled_rdesc_puck));
+ return sizeof(disabled_rdesc_puck);
+ }
+
+ return 0;
+}
+
+SEC(HID_BPF_DEVICE_EVENT)
+int BPF_PROG(k20_bt_fix_events, struct hid_bpf_ctx *hctx)
+{
+ __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 12 /* size */);
+ struct pad_report {
+ __u8 report_id;
+ __u8 btn_stylus:1;
+ __u8 pad:7;
+ __u8 x;
+ __u8 y;
+ __u32 buttons;
+ __u8 wheel;
+ } __packed * pad_report = (struct pad_report *)data;
+
+ if (!data)
+ return 0; /* EPERM check */
+
+ /* Report ID 1 - Keyboard events (button presses) */
+ if (data[0] == BT_PAD_KBD_REPORT_ID) {
+ const __u8 button_mapping[] = {
+ 0x0e, /* Button 1: K */
+ 0x0a, /* Button 2: G */
+ 0x0f, /* Button 3: L */
+ 0x4c, /* Button 4: Delete */
+ 0x0c, /* Button 5: I */
+ 0x07, /* Button 6: D */
+ 0x05, /* Button 7: B */
+ 0x08, /* Button 8: E */
+ 0x16, /* Button 9: S */
+ 0x1d, /* Button 10: Z */
+ 0x06, /* Button 11: C */
+ 0x19, /* Button 12: V */
+ 0xff, /* Button 13: LeftControl */
+ 0xff, /* Button 14: LeftAlt */
+ 0xff, /* Button 15: LeftShift */
+ 0x28, /* Button 16: Return Enter */
+ 0x2c, /* Button 17: Spacebar */
+ 0x11, /* Button 18: N */
+ };
+
+ __u8 modifiers = data[1];
+ __u32 buttons = 0;
+
+ if (modifiers & 0x01) { /* Control */
+ buttons |= BIT(12);
+ }
+ if (modifiers & 0x02) { /* Shift */
+ buttons |= BIT(14);
+ }
+ if (modifiers & 0x04) { /* Alt */
+ buttons |= BIT(13);
+ }
+
+ for (int i = 4; i < BT_PAD_KBD_REPORT_LENGTH; i++) {
+ if (!data[i])
+ break;
+
+ for (size_t b = 0; b < ARRAY_SIZE(button_mapping); b++) {
+ if (data[i] != 0xff && data[i] == button_mapping[b]) {
+ buttons |= BIT(b);
+ break;
+ }
+ }
+ }
+
+ last_button_state = buttons;
+
+ pad_report->report_id = OUR_REPORT_ID;
+ pad_report->btn_stylus = 0;
+ pad_report->x = 0;
+ pad_report->y = 0;
+ pad_report->buttons = buttons;
+ pad_report->wheel = 0;
+
+ return sizeof(struct pad_report);
+ }
+
+ /* Report ID 2 - Consumer control events (the button inside the wheel) */
+ if (data[0] == BT_PAD_CC_REPORT_ID) {
+ const __u8 PlayPause = 0xcd;
+
+ if (data[1] == PlayPause)
+ last_button_state |= BIT(18);
+ else
+ last_button_state &= ~BIT(18);
+
+ pad_report->report_id = OUR_REPORT_ID;
+ pad_report->btn_stylus = 0;
+ pad_report->x = 0;
+ pad_report->y = 0;
+ pad_report->buttons = last_button_state;
+ pad_report->wheel = 0;
+
+ return sizeof(struct pad_report);
+ }
+
+ /* Report ID 5 - Mouse events (wheel rotation) */
+ if (data[0] == BT_PAD_MOUSE_REPORT_ID) {
+ __u8 wheel_delta = data[6];
+
+ pad_report->report_id = OUR_REPORT_ID;
+ pad_report->btn_stylus = 0;
+ pad_report->x = 0;
+ pad_report->y = 0;
+ pad_report->buttons = last_button_state;
+ pad_report->wheel = wheel_delta;
+
+ return sizeof(struct pad_report);
+ }
+
+ return 0;
+}
+
+HID_BPF_OPS(keydial_k20_bluetooth) = {
+ .hid_device_event = (void *)k20_bt_fix_events,
+ .hid_rdesc_fixup = (void *)k20_bt_fix_rdesc,
+};
+
+SEC("syscall")
+int probe(struct hid_bpf_probe_args *ctx)
+{
+ switch (ctx->rdesc_size) {
+ case BT_PAD_REPORT_DESCRIPTOR_LENGTH:
+ case BT_PUCK_REPORT_DESCRIPTOR_LENGTH:
+ ctx->retval = 0;
+ break;
+ default:
+ ctx->retval = -EINVAL;
+ }
+
+ return 0;
+}
+
+char _license[] SEC("license") = "GPL";
--
2.53.0