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// 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_MICROSOFT 0x045e
#define PID_XBOX_ELITE_2 0x0b22
HID_BPF_CONFIG(
HID_DEVICE(BUS_BLUETOOTH, HID_GROUP_GENERIC, VID_MICROSOFT, PID_XBOX_ELITE_2)
);
/*
* When using the Xbox Wireless Controller Elite 2 over Bluetooth,
* the device exports the paddles on the back of the device as a single
* bitfield value of usage "Assign Selection".
*
* The kernel doesn't process the paddles usage properly and reports KEY_UNKNOWN.
*
* SDL doesn't know how to interpret KEY_UNKNOWN and thus ignores the paddles.
*
* Given that over USB the kernel uses BTN_TRIGGER_HAPPY[5-8], we
* can tweak the report descriptor to make the kernel interpret it properly:
* - We need an application collection of gamepad (so we have to close the current
* Consumer Control one)
* - We need to change the usage to be buttons from 0x15 to 0x18
*/
#define OFFSET_ASSIGN_SELECTION 211
#define ORIGINAL_RDESC_SIZE 464
const __u8 rdesc_assign_selection[] = {
0x0a, 0x99, 0x00, // Usage (Media Select Security) 211
0x15, 0x00, // Logical Minimum (0) 214
0x26, 0xff, 0x00, // Logical Maximum (255) 216
0x95, 0x01, // Report Count (1) 219
0x75, 0x04, // Report Size (4) 221
0x81, 0x02, // Input (Data,Var,Abs) 223
0x15, 0x00, // Logical Minimum (0) 225
0x25, 0x00, // Logical Maximum (0) 227
0x95, 0x01, // Report Count (1) 229
0x75, 0x04, // Report Size (4) 231
0x81, 0x03, // Input (Cnst,Var,Abs) 233
0x0a, 0x81, 0x00, // Usage (Assign Selection) 235
0x15, 0x00, // Logical Minimum (0) 238
0x26, 0xff, 0x00, // Logical Maximum (255) 240
0x95, 0x01, // Report Count (1) 243
0x75, 0x04, // Report Size (4) 245
0x81, 0x02, // Input (Data,Var,Abs) 247
};
/*
* we replace the above report descriptor extract
* with the one below.
* To make things equal in size, we take out a larger
* portion than just the "Assign Selection" range, because
* we need to insert a new application collection to force
* the kernel to use BTN_TRIGGER_HAPPY[4-7].
*/
const __u8 fixed_rdesc_assign_selection[] = {
0x0a, 0x99, 0x00, // Usage (Media Select Security) 211
0x15, 0x00, // Logical Minimum (0) 214
0x26, 0xff, 0x00, // Logical Maximum (255) 216
0x95, 0x01, // Report Count (1) 219
0x75, 0x04, // Report Size (4) 221
0x81, 0x02, // Input (Data,Var,Abs) 223
/* 0x15, 0x00, */ // Logical Minimum (0) ignored
0x25, 0x01, // Logical Maximum (1) 225
0x95, 0x04, // Report Count (4) 227
0x75, 0x01, // Report Size (1) 229
0x81, 0x03, // Input (Cnst,Var,Abs) 231
0xc0, // End Collection 233
0x05, 0x01, // Usage Page (Generic Desktop) 234
0x0a, 0x05, 0x00, // Usage (Game Pad) 236
0xa1, 0x01, // Collection (Application) 239
0x05, 0x09, // Usage Page (Button) 241
0x19, 0x15, // Usage Minimum (21) 243
0x29, 0x18, // Usage Maximum (24) 245
/* 0x15, 0x00, */ // Logical Minimum (0) ignored
/* 0x25, 0x01, */ // Logical Maximum (1) ignored
/* 0x95, 0x01, */ // Report Size (1) ignored
/* 0x75, 0x04, */ // Report Count (4) ignored
0x81, 0x02, // Input (Data,Var,Abs) 247
};
_Static_assert(sizeof(rdesc_assign_selection) == sizeof(fixed_rdesc_assign_selection),
"Rdesc and fixed rdesc of different size");
_Static_assert(sizeof(rdesc_assign_selection) + OFFSET_ASSIGN_SELECTION < ORIGINAL_RDESC_SIZE,
"Rdesc at given offset is too big");
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 */
/* Check that the device is compatible */
if (__builtin_memcmp(data + OFFSET_ASSIGN_SELECTION,
rdesc_assign_selection,
sizeof(rdesc_assign_selection)))
return 0;
__builtin_memcpy(data + OFFSET_ASSIGN_SELECTION,
fixed_rdesc_assign_selection,
sizeof(fixed_rdesc_assign_selection));
return 0;
}
HID_BPF_OPS(xbox_elite_2) = {
.hid_rdesc_fixup = (void *)hid_fix_rdesc,
};
SEC("syscall")
int probe(struct hid_bpf_probe_args *ctx)
{
/* only bind to the keyboard interface */
ctx->retval = ctx->rdesc_size != ORIGINAL_RDESC_SIZE;
if (ctx->retval)
ctx->retval = -EINVAL;
if (__builtin_memcmp(ctx->rdesc + OFFSET_ASSIGN_SELECTION,
rdesc_assign_selection,
sizeof(rdesc_assign_selection)))
ctx->retval = -EINVAL;
return 0;
}
char _license[] SEC("license") = "GPL";
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