/* 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 */