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| 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 | + */ |
| 82 | +struct 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 | + */ |
| 97 | +struct 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 */ |
| 106 | +struct 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 */ |
| 114 | +struct 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 */ |
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