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// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2024 Kumar Swarnam Iyer (kumar.s.iyer65@gmail.com)
*/
#include "vmlinux.h"
#include "hid_bpf.h"
#include "hid_bpf_helpers.h"
#include <bpf/bpf_tracing.h>
#define VID_THRUSTMASTER 0x044F
#define PID_TCA_YOKE_BOEING 0x0409
HID_BPF_CONFIG(
HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_THRUSTMASTER, PID_TCA_YOKE_BOEING)
);
/* The original HID descriptor of the Thrustmaster TCA Yoke Boeing joystick contains
* an Input field that shows up as an axis, ABS_MISC in Linux. But it is not possible
* to assign an actual physical control to this axis as they're all taken up. There
* are 2 vendor-defined inputs where the Input type appears to be defined wrongly.
* This bpf attempts to fix this by changing the Inputs so that it doesn't show up in
* Linux at all.
* This version is the short version fix that only changes 2 fields in the descriptor
* instead of the whole report descriptor.
* For reference, this is the original report descriptor:
*
* 0x05, 0x01, // Usage Page (Generic Desktop) 0
* 0x09, 0x04, // Usage (Joystick) 2
* 0xa1, 0x01, // Collection (Application) 4
* 0x85, 0x01, // Report ID (1) 6
* 0x09, 0x39, // Usage (Hat switch) 8
* 0x15, 0x00, // Logical Minimum (0) 10
* 0x25, 0x07, // Logical Maximum (7) 12
* 0x35, 0x00, // Physical Minimum (0) 14
* 0x46, 0x3b, 0x01, // Physical Maximum (315) 16
* 0x65, 0x14, // Unit (EnglishRotation: deg) 19
* 0x75, 0x04, // Report Size (4) 21
* 0x95, 0x01, // Report Count (1) 23
* 0x81, 0x42, // Input (Data,Var,Abs,Null) 25
* 0x65, 0x00, // Unit (None) 27
* 0x05, 0x09, // Usage Page (Button) 29
* 0x19, 0x01, // Usage Minimum (1) 31
* 0x29, 0x12, // Usage Maximum (18) 33
* 0x15, 0x00, // Logical Minimum (0) 35
* 0x25, 0x01, // Logical Maximum (1) 37
* 0x75, 0x01, // Report Size (1) 39
* 0x95, 0x12, // Report Count (18) 41
* 0x81, 0x02, // Input (Data,Var,Abs) 43
* 0x95, 0x02, // Report Count (2) 45
* 0x81, 0x03, // Input (Cnst,Var,Abs) 47
* 0x05, 0x01, // Usage Page (Generic Desktop) 49
* 0x09, 0x31, // Usage (Y) 51
* 0x09, 0x30, // Usage (X) 53
* 0x09, 0x32, // Usage (Z) 55
* 0x09, 0x34, // Usage (Ry) 57
* 0x09, 0x33, // Usage (Rx) 59
* 0x09, 0x35, // Usage (Rz) 61
* 0x15, 0x00, // Logical Minimum (0) 63
* 0x27, 0xff, 0xff, 0x00, 0x00, // Logical Maximum (65535) 65
* 0x75, 0x10, // Report Size (16) 70
* 0x95, 0x06, // Report Count (6) 72
* 0x81, 0x02, // Input (Data,Var,Abs) 74
* 0x06, 0xf0, 0xff, // Usage Page (Vendor Usage Page 0xfff0) 76
* 0x09, 0x59, // Usage (Vendor Usage 0x59) 79
* 0x15, 0x00, // Logical Minimum (0) 81
* 0x26, 0xff, 0x00, // Logical Maximum (255) 83
* 0x75, 0x08, // Report Size (8) 86
* 0x95, 0x01, // Report Count (1) 88
* 0x81, 0x02, // Input (Data,Var,Abs) 90 --> Needs to be changed
* 0x09, 0x51, // Usage (Vendor Usage 0x51) 92
* 0x15, 0x00, // Logical Minimum (0) 94
* 0x26, 0xff, 0x00, // Logical Maximum (255) 96
* 0x75, 0x08, // Report Size (8) 99
* 0x95, 0x20, // Report Count (32) 101 --> Needs to be changed
* 0x81, 0x02, // Input (Data,Var,Abs) 103
* 0x09, 0x50, // Usage (Vendor Usage 0x50) 105
* 0x15, 0x00, // Logical Minimum (0) 107
* 0x26, 0xff, 0x00, // Logical Maximum (255) 109
* 0x75, 0x08, // Report Size (8) 112
* 0x95, 0x0f, // Report Count (15) 114
* 0x81, 0x03, // Input (Cnst,Var,Abs) 116
* 0x09, 0x47, // Usage (Vendor Usage 0x47) 118
* 0x85, 0xf2, // Report ID (242) 120
* 0x15, 0x00, // Logical Minimum (0) 122
* 0x26, 0xff, 0x00, // Logical Maximum (255) 124
* 0x75, 0x08, // Report Size (8) 127
* 0x95, 0x3f, // Report Count (63) 129
* 0xb1, 0x02, // Feature (Data,Var,Abs) 131
* 0x09, 0x48, // Usage (Vendor Usage 0x48) 133
* 0x85, 0xf3, // Report ID (243) 135
* 0x15, 0x00, // Logical Minimum (0) 137
* 0x26, 0xff, 0x00, // Logical Maximum (255) 139
* 0x75, 0x08, // Report Size (8) 142
* 0x95, 0x3f, // Report Count (63) 144
* 0xb1, 0x02, // Feature (Data,Var,Abs) 146
* 0xc0, // End Collection 148
*/
SEC(HID_BPF_RDESC_FIXUP)
int BPF_PROG(hid_fix_rdesc_tca_yoke, struct hid_bpf_ctx *hctx)
{
const int expected_length = 148;
if (hctx->size != expected_length)
return 0;
__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, HID_MAX_DESCRIPTOR_SIZE /* size */);
if (!data)
return 0; /* EPERM */
/* Safety check, our probe() should take care of this though */
if (data[1] != 0x01 /* Generic Desktop */ || data[3] != 0x04 /* Joystick */)
return 0;
/* The report descriptor sets incorrect Input items in 2 places, resulting in a
* non-existing axis showing up.
* This change sets the correct Input which prevents the axis from showing up in Linux.
*/
if (data[90] == 0x81 && /* Input */
data[103] == 0x81) { /* Input */
data[91] = 0x03; /* Input set to 0x03 Constant, Variable Absolute */
data[104] = 0x03; /* Input set to 0X03 Constant, Variable Absolute */
}
return 0;
}
HID_BPF_OPS(tca_yoke) = {
.hid_rdesc_fixup = (void *)hid_fix_rdesc_tca_yoke,
};
SEC("syscall")
int probe(struct hid_bpf_probe_args *ctx)
{
/* ensure the kernel isn't fixed already */
if (ctx->rdesc[91] != 0x02) /* Input for 0x59 Usage type has changed */
ctx->retval = -EINVAL;
return 0;
}
char _license[] SEC("license") = "GPL";
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