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Benjamin Tissoires
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HID: bpf: Fix NKRO on Mistel MD770
Mistel MD770 keyboard (using Holtek Semiconductor, Inc. controller) has a quirk in report descriptor in one of its interfaces (more detail in the source file). Fix up the descriptor to allow NKRO to work again. Tested by loading the BPF program and confirming that 8 simultaneous keypresses work. Link: https://bugzilla.kernel.org/show_bug.cgi?id=218495 Link: https://gitlab.freedesktop.org/libevdev/udev-hid-bpf/-/merge_requests/122 Signed-off-by: Tatsuyuki Ishi <ishitatsuyuki@gmail.com> Acked-by: Jiri Kosina <jkosina@suse.com> Link: https://patch.msgid.link/20241017-import_bpf_6-13-v2-1-6a7acb89a97f@kernel.org Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
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‎drivers/hid/bpf/progs/Mistel__MD770.bpf.c‎

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// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2024 Tatsuyuki Ishi
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*/
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#include "vmlinux.h"
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#include "hid_bpf.h"
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#include "hid_bpf_helpers.h"
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#include <bpf/bpf_tracing.h>
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#define VID_HOLTEK 0x04D9
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#define PID_MD770 0x0339
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#define RDESC_SIZE 203
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HID_BPF_CONFIG(
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HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_HOLTEK, PID_MD770)
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);
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/*
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* The Mistel MD770 keyboard reports the first 6 simultaneous key presses
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* through the first interface, and anything beyond that through a second
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* interface. Unfortunately, the second interface's report descriptor has an
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* error, causing events to be malformed and ignored. This HID-BPF driver
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* fixes the descriptor to allow NKRO to work again.
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*
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* For reference, this is the original report descriptor:
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*
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* 0x05, 0x01, // Usage Page (Generic Desktop) 0
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* 0x09, 0x80, // Usage (System Control) 2
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* 0xa1, 0x01, // Collection (Application) 4
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* 0x85, 0x01, // Report ID (1) 6
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* 0x19, 0x81, // Usage Minimum (129) 8
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* 0x29, 0x83, // Usage Maximum (131) 10
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* 0x15, 0x00, // Logical Minimum (0) 12
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* 0x25, 0x01, // Logical Maximum (1) 14
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* 0x95, 0x03, // Report Count (3) 16
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* 0x75, 0x01, // Report Size (1) 18
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* 0x81, 0x02, // Input (Data,Var,Abs) 20
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* 0x95, 0x01, // Report Count (1) 22
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* 0x75, 0x05, // Report Size (5) 24
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* 0x81, 0x01, // Input (Cnst,Arr,Abs) 26
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* 0xc0, // End Collection 28
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* 0x05, 0x0c, // Usage Page (Consumer Devices) 29
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* 0x09, 0x01, // Usage (Consumer Control) 31
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* 0xa1, 0x01, // Collection (Application) 33
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* 0x85, 0x02, // Report ID (2) 35
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* 0x15, 0x00, // Logical Minimum (0) 37
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* 0x25, 0x01, // Logical Maximum (1) 39
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* 0x95, 0x12, // Report Count (18) 41
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* 0x75, 0x01, // Report Size (1) 43
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* 0x0a, 0x83, 0x01, // Usage (AL Consumer Control Config) 45
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* 0x0a, 0x8a, 0x01, // Usage (AL Email Reader) 48
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* 0x0a, 0x92, 0x01, // Usage (AL Calculator) 51
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* 0x0a, 0x94, 0x01, // Usage (AL Local Machine Browser) 54
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* 0x09, 0xcd, // Usage (Play/Pause) 57
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* 0x09, 0xb7, // Usage (Stop) 59
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* 0x09, 0xb6, // Usage (Scan Previous Track) 61
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* 0x09, 0xb5, // Usage (Scan Next Track) 63
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* 0x09, 0xe2, // Usage (Mute) 65
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* 0x09, 0xea, // Usage (Volume Down) 67
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* 0x09, 0xe9, // Usage (Volume Up) 69
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* 0x0a, 0x21, 0x02, // Usage (AC Search) 71
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* 0x0a, 0x23, 0x02, // Usage (AC Home) 74
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* 0x0a, 0x24, 0x02, // Usage (AC Back) 77
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* 0x0a, 0x25, 0x02, // Usage (AC Forward) 80
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* 0x0a, 0x26, 0x02, // Usage (AC Stop) 83
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* 0x0a, 0x27, 0x02, // Usage (AC Refresh) 86
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* 0x0a, 0x2a, 0x02, // Usage (AC Bookmarks) 89
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* 0x81, 0x02, // Input (Data,Var,Abs) 92
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* 0x95, 0x01, // Report Count (1) 94
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* 0x75, 0x0e, // Report Size (14) 96
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* 0x81, 0x01, // Input (Cnst,Arr,Abs) 98
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* 0xc0, // End Collection 100
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* 0x05, 0x01, // Usage Page (Generic Desktop) 101
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* 0x09, 0x02, // Usage (Mouse) 103
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* 0xa1, 0x01, // Collection (Application) 105
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* 0x09, 0x01, // Usage (Pointer) 107
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* 0xa1, 0x00, // Collection (Physical) 109
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* 0x85, 0x03, // Report ID (3) 111
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* 0x05, 0x09, // Usage Page (Button) 113
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* 0x19, 0x01, // Usage Minimum (1) 115
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* 0x29, 0x08, // Usage Maximum (8) 117
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* 0x15, 0x00, // Logical Minimum (0) 119
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* 0x25, 0x01, // Logical Maximum (1) 121
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* 0x75, 0x01, // Report Size (1) 123
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* 0x95, 0x08, // Report Count (8) 125
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* 0x81, 0x02, // Input (Data,Var,Abs) 127
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* 0x05, 0x01, // Usage Page (Generic Desktop) 129
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* 0x09, 0x30, // Usage (X) 131
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* 0x09, 0x31, // Usage (Y) 133
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* 0x16, 0x01, 0x80, // Logical Minimum (-32767) 135
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* 0x26, 0xff, 0x7f, // Logical Maximum (32767) 138
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* 0x75, 0x10, // Report Size (16) 141
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* 0x95, 0x02, // Report Count (2) 143
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* 0x81, 0x06, // Input (Data,Var,Rel) 145
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* 0x09, 0x38, // Usage (Wheel) 147
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* 0x15, 0x81, // Logical Minimum (-127) 149
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* 0x25, 0x7f, // Logical Maximum (127) 151
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* 0x75, 0x08, // Report Size (8) 153
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* 0x95, 0x01, // Report Count (1) 155
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* 0x81, 0x06, // Input (Data,Var,Rel) 157
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* 0x05, 0x0c, // Usage Page (Consumer Devices) 159
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* 0x0a, 0x38, 0x02, // Usage (AC Pan) 161
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* 0x95, 0x01, // Report Count (1) 164
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* 0x81, 0x06, // Input (Data,Var,Rel) 166
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* 0xc0, // End Collection 168
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* 0xc0, // End Collection 169
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* 0x05, 0x01, // Usage Page (Generic Desktop) 170
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* 0x09, 0x06, // Usage (Keyboard) 172
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* 0xa1, 0x01, // Collection (Application) 174
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* 0x85, 0x04, // Report ID (4) 176
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* 0x05, 0x07, // Usage Page (Keyboard) 178
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* 0x95, 0x01, // Report Count (1) 180
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* 0x75, 0x08, // Report Size (8) 182
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* 0x81, 0x03, // Input (Cnst,Var,Abs) 184
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* 0x95, 0xe8, // Report Count (232) 186
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* 0x75, 0x01, // Report Size (1) 188
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* 0x15, 0x00, // Logical Minimum (0) 190
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* 0x25, 0x01, // Logical Maximum (1) 192
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* 0x05, 0x07, // Usage Page (Keyboard) 194
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* 0x19, 0x00, // Usage Minimum (0) 196
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* 0x29, 0xe7, // Usage Maximum (231) 198
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* 0x81, 0x00, // Input (Data,Arr,Abs) 200 <- change to 0x81, 0x02 (Data,Var,Abs)
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* 0xc0, // End Collection 202
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*/
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SEC(HID_BPF_RDESC_FIXUP)
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int BPF_PROG(hid_rdesc_fixup_mistel_md770, struct hid_bpf_ctx *hctx)
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{
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__u8 *data = hid_bpf_get_data(hctx, 0, HID_MAX_DESCRIPTOR_SIZE);
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if (!data)
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return 0; /* EPERM check */
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if (data[201] == 0x00)
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data[201] = 0x02;
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return 0;
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}
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HID_BPF_OPS(mistel_md770) = {
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.hid_rdesc_fixup = (void *)hid_rdesc_fixup_mistel_md770,
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};
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SEC("syscall")
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int probe(struct hid_bpf_probe_args *ctx)
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{
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ctx->retval = ctx->rdesc_size != RDESC_SIZE;
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if (ctx->retval)
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ctx->retval = -EINVAL;
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return 0;
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}
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char _license[] SEC("license") = "GPL";

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