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  * @con_priv: Hook for controller driver to attach private data
48  *
49  * Currently, the mailbox API assumes that a single integer ID is enough to
50  * identify and configure any mailbox channel for any mailbox provider. If this
51  * assumption becomes invalid in the future, the struct could be expanded to
52  * either (a) add more fields to allow mailbox providers to store additional
53  * information, or (b) replace the id field with an opaque pointer, which the
54  * provider would dynamically allocated during its .of_xlate op, and process
55  * during is .request op. This may require the addition of an extra op to clean
56  * up the allocation.
57  */
58 struct mbox_chan {
59 	struct udevice *dev;
60 	/* Written by of_xlate.*/
61 	unsigned long id;
62 	void *con_priv;
63 };
64 
65 /**
66  * mbox_get_by_index - Get/request a mailbox by integer index
67  *
68  * This looks up and requests a mailbox channel. The index is relative to the
69  * client device; each device is assumed to have n mailbox channels associated
70  * with it somehow, and this function finds and requests one of them. The
71  * mapping of client device channel indices to provider channels may be via
72  * device-tree properties, board-provided mapping tables, or some other
73  * mechanism.
74  *
75  * @dev:	The client device.
76  * @index:	The index of the mailbox channel to request, within the
77  *		client's list of channels.
78  * @chan	A pointer to a channel object to initialize.
79  * @return 0 if OK, or a negative error code.
80  */
81 int mbox_get_by_index(struct udevice *dev, int index, struct mbox_chan *chan);
82 
83 /**
84  * mbox_get_by_name - Get/request a mailbox by name
85  *
86  * This looks up and requests a mailbox channel. The name is relative to the
87  * client device; each device is assumed to have n mailbox channels associated
88  * with it somehow, and this function finds and requests one of them. The
89  * mapping of client device channel names to provider channels may be via
90  * device-tree properties, board-provided mapping tables, or some other
91  * mechanism.
92  *
93  * @dev:	The client device.
94  * @name:	The name of the mailbox channel to request, within the client's
95  *		list of channels.
96  * @chan	A pointer to a channel object to initialize.
97  * @return 0 if OK, or a negative error code.
98  */
99 int mbox_get_by_name(struct udevice *dev, const char *name,
100 		     struct mbox_chan *chan);
101 
102 /**
103  * mbox_free - Free a previously requested mailbox channel.
104  *
105  * @chan:	A channel object that was previously successfully requested by
106  *		calling mbox_get_by_*().
107  * @return 0 if OK, or a negative error code.
108  */
109 int mbox_free(struct mbox_chan *chan);
110 
111 /**
112  * mbox_send - Send a message over a mailbox channel
113  *
114  * This function will send a message to the remote entity. It may return before
115  * the remote entity has received and/or processed the message.
116  *
117  * @chan:	A channel object that was previously successfully requested by
118  *		calling mbox_get_by_*().
119  * @data:	A pointer to the message to transfer. The format and size of
120  *		the memory region pointed at by @data is determined by the
121  *		mailbox provider. Providers that solely transfer notifications
122  *		will ignore this parameter.
123  * @return 0 if OK, or a negative error code.
124  */
125 int mbox_send(struct mbox_chan *chan, const void *data);
126 
127 /**
128  * mbox_recv - Receive any available message from a mailbox channel
129  *
130  * This function will wait (up to the specified @timeout_us) for a message to
131  * be sent by the remote entity, and write the content of any such message
132  * into a caller-provided buffer.
133  *
134  * @chan:	A channel object that was previously successfully requested by
135  *		calling mbox_get_by_*().
136  * @data:	A pointer to the buffer to receive the message. The format and
137  *		size of the memory region pointed at by @data is determined by
138  *		the mailbox provider. Providers that solely transfer
139  *		notifications will ignore this parameter.
140  * @timeout_us:	The maximum time to wait for a message to be available, in
141  *		micro-seconds. A value of 0 does not wait at all.
142  * @return 0 if OK, -ENODATA if no message was available, or a negative error
143  * code.
144  */
145 int mbox_recv(struct mbox_chan *chan, void *data, ulong timeout_us);
146 
147 #endif
148