1 /* SPDX-License-Identifier: GPL-2.0 */ 2 /* 3 * Copyright (c) 2016, NVIDIA CORPORATION. 4 */ 5 6 #ifndef _MAILBOX_H 7 #define _MAILBOX_H 8 9 /** 10 * A mailbox is a hardware mechanism for transferring small fixed-size messages 11 * and/or notifications between the CPU on which U-Boot runs and some other 12 * device such as an auxiliary CPU running firmware or a hardware module. 13 * 14 * Data transfer is optional; a mailbox may consist solely of a notification 15 * mechanism. When data transfer is implemented, it is via HW registers or 16 * FIFOs, rather than via RAM-based buffers. The mailbox API generally 17 * implements any communication protocol enforced solely by hardware, and 18 * leaves any higher-level protocols to other layers. 19 * 20 * A mailbox channel is a bi-directional mechanism that can send a message or 21 * notification to a single specific remote entity, and receive messages or 22 * notifications from that entity. The size, content, and format of such 23 * messages is defined by the mailbox implementation, or the remote entity with 24 * which it communicates; there is no general standard at this API level. 25 * 26 * A driver that implements UCLASS_MAILBOX is a mailbox provider. A provider 27 * will often implement multiple separate mailbox channels, since the hardware 28 * it manages often has this capability. mailbox-uclass.h describes the 29 * interface which mailbox providers must implement. 30 * 31 * Mailbox consumers/clients generate and send, or receive and process, 32 * messages. This header file describes the API used by clients. 33 */ 34 35 struct udevice; 36 37 /** 38 * struct mbox_chan - A handle to a single mailbox channel. 39 * 40 * Clients provide storage for channels. The content of the channel structure 41 * is managed solely by the mailbox API and mailbox drivers. A mailbox channel 42 * is initialized by "get"ing the mailbox. The channel struct is passed to all 43 * other mailbox APIs to identify which mailbox to operate upon. 44 * 45 * @dev: The device which implements the mailbox. 46 * @id: The mailbox channel ID within the provider. 47 * 48 * Currently, the mailbox API assumes that a single integer ID is enough to 49 * identify and configure any mailbox channel for any mailbox provider. If this 50 * assumption becomes invalid in the future, the struct could be expanded to 51 * either (a) add more fields to allow mailbox providers to store additional 52 * information, or (b) replace the id field with an opaque pointer, which the 53 * provider would dynamically allocated during its .of_xlate op, and process 54 * during is .request op. This may require the addition of an extra op to clean 55 * up the allocation. 56 */ 57 struct mbox_chan { 58 struct udevice *dev; 59 /* 60 * Written by of_xlate. We assume a single id is enough for now. In the 61 * future, we might add more fields here. 62 */ 63 unsigned long id; 64 }; 65 66 /** 67 * mbox_get_by_index - Get/request a mailbox by integer index 68 * 69 * This looks up and requests a mailbox channel. The index is relative to the 70 * client device; each device is assumed to have n mailbox channels associated 71 * with it somehow, and this function finds and requests one of them. The 72 * mapping of client device channel indices to provider channels may be via 73 * device-tree properties, board-provided mapping tables, or some other 74 * mechanism. 75 * 76 * @dev: The client device. 77 * @index: The index of the mailbox channel to request, within the 78 * client's list of channels. 79 * @chan A pointer to a channel object to initialize. 80 * @return 0 if OK, or a negative error code. 81 */ 82 int mbox_get_by_index(struct udevice *dev, int index, struct mbox_chan *chan); 83 84 /** 85 * mbox_get_by_name - Get/request a mailbox by name 86 * 87 * This looks up and requests a mailbox channel. The name is relative to the 88 * client device; each device is assumed to have n mailbox channels associated 89 * with it somehow, and this function finds and requests one of them. The 90 * mapping of client device channel names to provider channels may be via 91 * device-tree properties, board-provided mapping tables, or some other 92 * mechanism. 93 * 94 * @dev: The client device. 95 * @name: The name of the mailbox channel to request, within the client's 96 * list of channels. 97 * @chan A pointer to a channel object to initialize. 98 * @return 0 if OK, or a negative error code. 99 */ 100 int mbox_get_by_name(struct udevice *dev, const char *name, 101 struct mbox_chan *chan); 102 103 /** 104 * mbox_free - Free a previously requested mailbox channel. 105 * 106 * @chan: A channel object that was previously successfully requested by 107 * calling mbox_get_by_*(). 108 * @return 0 if OK, or a negative error code. 109 */ 110 int mbox_free(struct mbox_chan *chan); 111 112 /** 113 * mbox_send - Send a message over a mailbox channel 114 * 115 * This function will send a message to the remote entity. It may return before 116 * the remote entity has received and/or processed the message. 117 * 118 * @chan: A channel object that was previously successfully requested by 119 * calling mbox_get_by_*(). 120 * @data: A pointer to the message to transfer. The format and size of 121 * the memory region pointed at by @data is determined by the 122 * mailbox provider. Providers that solely transfer notifications 123 * will ignore this parameter. 124 * @return 0 if OK, or a negative error code. 125 */ 126 int mbox_send(struct mbox_chan *chan, const void *data); 127 128 /** 129 * mbox_recv - Receive any available message from a mailbox channel 130 * 131 * This function will wait (up to the specified @timeout_us) for a message to 132 * be sent by the remote entity, and write the content of any such message 133 * into a caller-provided buffer. 134 * 135 * @chan: A channel object that was previously successfully requested by 136 * calling mbox_get_by_*(). 137 * @data: A pointer to the buffer to receive the message. The format and 138 * size of the memory region pointed at by @data is determined by 139 * the mailbox provider. Providers that solely transfer 140 * notifications will ignore this parameter. 141 * @timeout_us: The maximum time to wait for a message to be available, in 142 * micro-seconds. A value of 0 does not wait at all. 143 * @return 0 if OK, -ENODATA if no message was available, or a negative error 144 * code. 145 */ 146 int mbox_recv(struct mbox_chan *chan, void *data, ulong timeout_us); 147 148 #endif 149