1/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
2/*
3 * Focusrite Control Protocol Driver for ALSA
4 *
5 * Copyright (c) 2024-2025 by Geoffrey D. Bennett <g at b4.vu>
6 */
7/*
8 * DOC: FCP (Focusrite Control Protocol) User-Space API
9 *
10 * This header defines the interface between the FCP kernel driver and
11 * user-space programs to enable the use of the proprietary features
12 * available in Focusrite USB audio interfaces. This includes Scarlett
13 * 2nd Gen, 3rd Gen, 4th Gen, Clarett USB, Clarett+, and Vocaster
14 * series devices.
15 *
16 * The interface is provided via ALSA's hwdep interface. Opening the
17 * hwdep device requires CAP_SYS_RAWIO privileges as this interface
18 * provides near-direct access.
19 *
20 * For details on the FCP protocol, refer to the kernel scarlett2
21 * driver in sound/usb/mixer_scarlett2.c and the fcp-support project
22 * at https://github.com/geoffreybennett/fcp-support
23 *
24 * For examples of using these IOCTLs, see the fcp-server source in
25 * the fcp-support project.
26 *
27 * IOCTL Interface
28 * --------------
29 * FCP_IOCTL_PVERSION:
30 * Returns the protocol version supported by the driver.
31 *
32 * FCP_IOCTL_INIT:
33 * Initialises the protocol and synchronises sequence numbers
34 * between the driver and device. Must be called at least once
35 * before sending commands. Can be safely called again at any time.
36 *
37 * FCP_IOCTL_CMD:
38 * Sends an FCP command to the device and returns the response.
39 * Requires prior initialisation via FCP_IOCTL_INIT.
40 *
41 * FCP_IOCTL_SET_METER_MAP:
42 * Configures the Level Meter control's mapping between device
43 * meters and control channels. Requires FCP_IOCTL_INIT to have been
44 * called first. The map size and number of slots cannot be changed
45 * after initial configuration, although the map itself can be
46 * updated. Once configured, the Level Meter remains functional even
47 * after the hwdep device is closed.
48 *
49 * FCP_IOCTL_SET_METER_LABELS:
50 * Set the labels for the Level Meter control. Requires
51 * FCP_IOCTL_SET_METER_MAP to have been called first. labels[]
52 * should contain a sequence of null-terminated labels corresponding
53 * to the control's channels.
54 */
55#ifndef __UAPI_SOUND_FCP_H
56#define __UAPI_SOUND_FCP_H
57
58#include <linux/types.h>
59#include <linux/ioctl.h>
60
61#define FCP_HWDEP_MAJOR 2
62#define FCP_HWDEP_MINOR 0
63#define FCP_HWDEP_SUBMINOR 0
64
65#define FCP_HWDEP_VERSION \
66 ((FCP_HWDEP_MAJOR << 16) | \
67 (FCP_HWDEP_MINOR << 8) | \
68 FCP_HWDEP_SUBMINOR)
69
70#define FCP_HWDEP_VERSION_MAJOR(v) (((v) >> 16) & 0xFF)
71#define FCP_HWDEP_VERSION_MINOR(v) (((v) >> 8) & 0xFF)
72#define FCP_HWDEP_VERSION_SUBMINOR(v) ((v) & 0xFF)
73
74/* Get protocol version */
75#define FCP_IOCTL_PVERSION _IOR('S', 0x60, int)
76
77/* Start the protocol */
78
79/* Step 0 and step 2 responses are variable length and placed in
80 * resp[] one after the other.
81 */
82struct fcp_init {
83 __u16 step0_resp_size;
84 __u16 step2_resp_size;
85 __u32 init1_opcode;
86 __u32 init2_opcode;
87 __u8 resp[];
88} __attribute__((packed));
89
90#define FCP_IOCTL_INIT _IOWR('S', 0x64, struct fcp_init)
91
92/* Perform a command */
93
94/* The request data is placed in data[] and the response data will
95 * overwrite it.
96 */
97struct fcp_cmd {
98 __u32 opcode;
99 __u16 req_size;
100 __u16 resp_size;
101 __u8 data[];
102} __attribute__((packed));
103#define FCP_IOCTL_CMD _IOWR('S', 0x65, struct fcp_cmd)
104
105/* Set the meter map */
106struct fcp_meter_map {
107 __u16 map_size;
108 __u16 meter_slots;
109 __s16 map[];
110} __attribute__((packed));
111#define FCP_IOCTL_SET_METER_MAP _IOW('S', 0x66, struct fcp_meter_map)
112
113/* Set the meter labels */
114struct fcp_meter_labels {
115 __u16 labels_size;
116 char labels[];
117} __attribute__((packed));
118#define FCP_IOCTL_SET_METER_LABELS _IOW('S', 0x67, struct fcp_meter_labels)
119
120#endif /* __UAPI_SOUND_FCP_H */