include/mailbox.h

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