Microsoft__Xbox-Elite-2.bpf.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/* Copyright (c) 2024 Benjamin Tissoires
  3 */
  4
  5#include "vmlinux.h"
  6#include "hid_bpf.h"
  7#include "hid_bpf_helpers.h"
  8#include <bpf/bpf_tracing.h>
  9
 10#define VID_MICROSOFT 0x045e
 11#define PID_XBOX_ELITE_2 0x0b22
 12
 13HID_BPF_CONFIG(
 14	HID_DEVICE(BUS_BLUETOOTH, HID_GROUP_GENERIC, VID_MICROSOFT, PID_XBOX_ELITE_2)
 15);
 16
 17/*
 18 * When using the Xbox Wireless Controller Elite 2 over Bluetooth,
 19 * the device exports the paddles on the back of the device as a single
 20 * bitfield value of usage "Assign Selection".
 21 *
 22 * The kernel doesn't process the paddles usage properly and reports KEY_UNKNOWN.
 23 *
 24 * SDL doesn't know how to interpret KEY_UNKNOWN and thus ignores the paddles.
 25 *
 26 * Given that over USB the kernel uses BTN_TRIGGER_HAPPY[5-8], we
 27 * can tweak the report descriptor to make the kernel interpret it properly:
 28 * - We need an application collection of gamepad (so we have to close the current
 29 *   Consumer Control one)
 30 * - We need to change the usage to be buttons from 0x15 to 0x18
 31 */
 32
 33#define OFFSET_ASSIGN_SELECTION		211
 34#define ORIGINAL_RDESC_SIZE		464
 35
 36const __u8 rdesc_assign_selection[] = {
 37	0x0a, 0x99, 0x00,              //   Usage (Media Select Security)     211
 38	0x15, 0x00,                    //   Logical Minimum (0)               214
 39	0x26, 0xff, 0x00,              //   Logical Maximum (255)             216
 40	0x95, 0x01,                    //   Report Count (1)                  219
 41	0x75, 0x04,                    //   Report Size (4)                   221
 42	0x81, 0x02,                    //   Input (Data,Var,Abs)              223
 43	0x15, 0x00,                    //   Logical Minimum (0)               225
 44	0x25, 0x00,                    //   Logical Maximum (0)               227
 45	0x95, 0x01,                    //   Report Count (1)                  229
 46	0x75, 0x04,                    //   Report Size (4)                   231
 47	0x81, 0x03,                    //   Input (Cnst,Var,Abs)              233
 48	0x0a, 0x81, 0x00,              //   Usage (Assign Selection)          235
 49	0x15, 0x00,                    //   Logical Minimum (0)               238
 50	0x26, 0xff, 0x00,              //   Logical Maximum (255)             240
 51	0x95, 0x01,                    //   Report Count (1)                  243
 52	0x75, 0x04,                    //   Report Size (4)                   245
 53	0x81, 0x02,                    //   Input (Data,Var,Abs)              247
 54};
 55
 56/*
 57 * we replace the above report descriptor extract
 58 * with the one below.
 59 * To make things equal in size, we take out a larger
 60 * portion than just the "Assign Selection" range, because
 61 * we need to insert a new application collection to force
 62 * the kernel to use BTN_TRIGGER_HAPPY[4-7].
 63 */
 64const __u8 fixed_rdesc_assign_selection[] = {
 65	0x0a, 0x99, 0x00,              //   Usage (Media Select Security)     211
 66	0x15, 0x00,                    //   Logical Minimum (0)               214
 67	0x26, 0xff, 0x00,              //   Logical Maximum (255)             216
 68	0x95, 0x01,                    //   Report Count (1)                  219
 69	0x75, 0x04,                    //   Report Size (4)                   221
 70	0x81, 0x02,                    //   Input (Data,Var,Abs)              223
 71	/* 0x15, 0x00, */              //   Logical Minimum (0)               ignored
 72	0x25, 0x01,                    //   Logical Maximum (1)               225
 73	0x95, 0x04,                    //   Report Count (4)                  227
 74	0x75, 0x01,                    //   Report Size (1)                   229
 75	0x81, 0x03,                    //   Input (Cnst,Var,Abs)              231
 76	0xc0,                          //  End Collection                     233
 77	0x05, 0x01,                    //  Usage Page (Generic Desktop)       234
 78	0x0a, 0x05, 0x00,              //  Usage (Game Pad)                   236
 79	0xa1, 0x01,                    //  Collection (Application)           239
 80	0x05, 0x09,                    //   Usage Page (Button)               241
 81	0x19, 0x15,                    //   Usage Minimum (21)                243
 82	0x29, 0x18,                    //   Usage Maximum (24)                245
 83	/* 0x15, 0x00, */              //  Logical Minimum (0)                ignored
 84	/* 0x25, 0x01, */              //  Logical Maximum (1)                ignored
 85	/* 0x95, 0x01, */              //  Report Size (1)                    ignored
 86	/* 0x75, 0x04, */              //  Report Count (4)                   ignored
 87	0x81, 0x02,                    //   Input (Data,Var,Abs)              247
 88};
 89
 90_Static_assert(sizeof(rdesc_assign_selection) == sizeof(fixed_rdesc_assign_selection),
 91	       "Rdesc and fixed rdesc of different size");
 92_Static_assert(sizeof(rdesc_assign_selection) + OFFSET_ASSIGN_SELECTION < ORIGINAL_RDESC_SIZE,
 93	       "Rdesc at given offset is too big");
 94
 95SEC(HID_BPF_RDESC_FIXUP)
 96int BPF_PROG(hid_fix_rdesc, struct hid_bpf_ctx *hctx)
 97{
 98	__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 4096 /* size */);
 99
100	if (!data)
101		return 0; /* EPERM check */
102
103	/* Check that the device is compatible */
104	if (__builtin_memcmp(data + OFFSET_ASSIGN_SELECTION,
105			     rdesc_assign_selection,
106			     sizeof(rdesc_assign_selection)))
107		return 0;
108
109	__builtin_memcpy(data + OFFSET_ASSIGN_SELECTION,
110			 fixed_rdesc_assign_selection,
111			 sizeof(fixed_rdesc_assign_selection));
112
113	return 0;
114}
115
116HID_BPF_OPS(xbox_elite_2) = {
117	.hid_rdesc_fixup = (void *)hid_fix_rdesc,
118};
119
120SEC("syscall")
121int probe(struct hid_bpf_probe_args *ctx)
122{
123	/* only bind to the keyboard interface */
124	ctx->retval = ctx->rdesc_size != ORIGINAL_RDESC_SIZE;
125	if (ctx->retval)
126		ctx->retval = -EINVAL;
127
128	if (__builtin_memcmp(ctx->rdesc + OFFSET_ASSIGN_SELECTION,
129			     rdesc_assign_selection,
130			     sizeof(rdesc_assign_selection)))
131		ctx->retval = -EINVAL;
132
133	return 0;
134}
135
136char _license[] SEC("license") = "GPL";