/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
/*
* Focusrite Control Protocol Driver for ALSA
*
* Copyright (c) 2024-2025 by Geoffrey D. Bennett <g at b4.vu>
*/
/*
* DOC: FCP (Focusrite Control Protocol) User-Space API
*
* This header defines the interface between the FCP kernel driver and
* user-space programs to enable the use of the proprietary features
* available in Focusrite USB audio interfaces. This includes Scarlett
* 2nd Gen, 3rd Gen, 4th Gen, Clarett USB, Clarett+, and Vocaster
* series devices.
*
* The interface is provided via ALSA's hwdep interface. Opening the
* hwdep device requires CAP_SYS_RAWIO privileges as this interface
* provides near-direct access.
*
* For details on the FCP protocol, refer to the kernel scarlett2
* driver in sound/usb/mixer_scarlett2.c and the fcp-support project
* at https://github.com/geoffreybennett/fcp-support
*
* For examples of using these IOCTLs, see the fcp-server source in
* the fcp-support project.
*
* IOCTL Interface
* --------------
* FCP_IOCTL_PVERSION:
* Returns the protocol version supported by the driver.
*
* FCP_IOCTL_INIT:
* Initialises the protocol and synchronises sequence numbers
* between the driver and device. Must be called at least once
* before sending commands. Can be safely called again at any time.
*
* FCP_IOCTL_CMD:
* Sends an FCP command to the device and returns the response.
* Requires prior initialisation via FCP_IOCTL_INIT.
*
* FCP_IOCTL_SET_METER_MAP:
* Configures the Level Meter control's mapping between device
* meters and control channels. Requires FCP_IOCTL_INIT to have been
* called first. The map size and number of slots cannot be changed
* after initial configuration, although the map itself can be
* updated. Once configured, the Level Meter remains functional even
* after the hwdep device is closed.
*
* FCP_IOCTL_SET_METER_LABELS:
* Set the labels for the Level Meter control. Requires
* FCP_IOCTL_SET_METER_MAP to have been called first. labels[]
* should contain a sequence of null-terminated labels corresponding
* to the control's channels.
*/
#ifndef __UAPI_SOUND_FCP_H
#define __UAPI_SOUND_FCP_H
#include <linux/types.h>
#include <linux/ioctl.h>
#define FCP_HWDEP_MAJOR 2
#define FCP_HWDEP_MINOR 0
#define FCP_HWDEP_SUBMINOR 0
#define FCP_HWDEP_VERSION \
((FCP_HWDEP_MAJOR << 16) | \
(FCP_HWDEP_MINOR << 8) | \
FCP_HWDEP_SUBMINOR)
#define FCP_HWDEP_VERSION_MAJOR(v) (((v) >> 16) & 0xFF)
#define FCP_HWDEP_VERSION_MINOR(v) (((v) >> 8) & 0xFF)
#define FCP_HWDEP_VERSION_SUBMINOR(v) ((v) & 0xFF)
/* Get protocol version */
#define FCP_IOCTL_PVERSION _IOR('S', 0x60, int)
/* Start the protocol */
/* Step 0 and step 2 responses are variable length and placed in
* resp[] one after the other.
*/
struct fcp_init {
__u16 step0_resp_size;
__u16 step2_resp_size;
__u32 init1_opcode;
__u32 init2_opcode;
__u8 resp[];
} __attribute__((packed));
#define FCP_IOCTL_INIT _IOWR('S', 0x64, struct fcp_init)
/* Perform a command */
/* The request data is placed in data[] and the response data will
* overwrite it.
*/
struct fcp_cmd {
__u32 opcode;
__u16 req_size;
__u16 resp_size;
__u8 data[];
} __attribute__((packed));
#define FCP_IOCTL_CMD _IOWR('S', 0x65, struct fcp_cmd)
/* Set the meter map */
struct fcp_meter_map {
__u16 map_size;
__u16 meter_slots;
__s16 map[];
} __attribute__((packed));
#define FCP_IOCTL_SET_METER_MAP _IOW('S', 0x66, struct fcp_meter_map)
/* Set the meter labels */
struct fcp_meter_labels {
__u16 labels_size;
char labels[];
} __attribute__((packed));
#define FCP_IOCTL_SET_METER_LABELS _IOW('S', 0x67, struct fcp_meter_labels)
#endif /* __UAPI_SOUND_FCP_H */
|