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+/*
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+ * Copyright (c) 2016, NVIDIA CORPORATION.
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+ *
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+ * SPDX-License-Identifier: GPL-2.0
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+ */
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+
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+#ifndef _MAILBOX_CLIENT_H
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+#define _MAILBOX_CLIENT_H
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+
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+/**
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+ * A mailbox is a hardware mechanism for transferring small fixed-size messages
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+ * and/or notifications between the CPU on which U-Boot runs and some other
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+ * device such as an auxiliary CPU running firmware or a hardware module.
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+ *
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+ * Data transfer is optional; a mailbox may consist solely of a notification
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+ * mechanism. When data transfer is implemented, it is via HW registers or
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+ * FIFOs, rather than via RAM-based buffers. The mailbox API generally
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+ * implements any communication protocol enforced solely by hardware, and
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+ * leaves any higher-level protocols to other layers.
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+ *
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+ * A mailbox channel is a bi-directional mechanism that can send a message or
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+ * notification to a single specific remote entity, and receive messages or
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+ * notifications from that entity. The size, content, and format of such
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+ * messages is defined by the mailbox implementation, or the remote entity with
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+ * which it communicates; there is no general standard at this API level.
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+ *
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+ * A driver that implements UCLASS_MAILBOX is a mailbox provider. A provider
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+ * will often implement multiple separate mailbox channels, since the hardware
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+ * it manages often has this capability. mailbox_uclass.h describes the
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+ * interface which mailbox providers must implement.
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+ *
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+ * Mailbox consumers/clients generate and send, or receive and process,
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+ * messages. This header file describes the API used by clients.
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+ */
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+
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+struct udevice;
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+
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+/**
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+ * struct mbox_chan - A handle to a single mailbox channel.
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+ *
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+ * Clients provide storage for channels. The content of the channel structure
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+ * is managed solely by the mailbox API and mailbox drivers. A mailbox channel
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+ * is initialized by "get"ing the mailbox. The channel struct is passed to all
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+ * other mailbox APIs to identify which mailbox to operate upon.
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+ *
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+ * @dev: The device which implements the mailbox.
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+ * @id: The mailbox channel ID within the provider.
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+ *
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+ * Currently, the mailbox API assumes that a single integer ID is enough to
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+ * identify and configure any mailbox channel for any mailbox provider. If this
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+ * assumption becomes invalid in the future, the struct could be expanded to
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+ * either (a) add more fields to allow mailbox providers to store additional
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+ * information, or (b) replace the id field with an opaque pointer, which the
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+ * provider would dynamically allocated during its .of_xlate op, and process
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+ * during is .request op. This may require the addition of an extra op to clean
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+ * up the allocation.
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+ */
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+struct mbox_chan {
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+ struct udevice *dev;
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+ /*
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+ * Written by of_xlate. We assume a single id is enough for now. In the
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+ * future, we might add more fields here.
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+ */
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+ unsigned long id;
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+};
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+
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+/**
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+ * mbox_get_by_index - Get/request a mailbox by integer index
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+ *
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+ * This looks up and requests a mailbox channel. The index is relative to the
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+ * client device; each device is assumed to have n mailbox channels associated
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+ * with it somehow, and this function finds and requests one of them. The
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+ * mapping of client device channel indices to provider channels may be via
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+ * device-tree properties, board-provided mapping tables, or some other
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+ * mechanism.
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+ *
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+ * @dev: The client device.
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+ * @index: The index of the mailbox channel to request, within the
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+ * client's list of channels.
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+ * @chan A pointer to a channel object to initialize.
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+ * @return 0 if OK, or a negative error code.
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+ */
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+int mbox_get_by_index(struct udevice *dev, int index, struct mbox_chan *chan);
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+
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+/**
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+ * mbox_get_by_name - Get/request a mailbox by name
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+ *
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+ * This looks up and requests a mailbox channel. The name is relative to the
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+ * client device; each device is assumed to have n mailbox channels associated
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+ * with it somehow, and this function finds and requests one of them. The
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+ * mapping of client device channel names to provider channels may be via
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+ * device-tree properties, board-provided mapping tables, or some other
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+ * mechanism.
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+ *
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+ * @dev: The client device.
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+ * @name: The name of the mailbox channel to request, within the client's
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+ * list of channels.
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+ * @chan A pointer to a channel object to initialize.
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+ * @return 0 if OK, or a negative error code.
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+ */
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+int mbox_get_by_name(struct udevice *dev, const char *name,
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+ struct mbox_chan *chan);
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+
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+/**
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+ * mbox_free - Free a previously requested mailbox channel.
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+ *
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+ * @chan: A channel object that was previously successfully requested by
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+ * calling mbox_get_by_*().
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+ * @return 0 if OK, or a negative error code.
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+ */
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+int mbox_free(struct mbox_chan *chan);
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+
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+/**
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+ * mbox_send - Send a message over a mailbox channel
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+ *
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+ * This function will send a message to the remote entity. It may return before
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+ * the remote entity has received and/or processed the message.
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+ *
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+ * @chan: A channel object that was previously successfully requested by
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+ * calling mbox_get_by_*().
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+ * @data: A pointer to the message to transfer. The format and size of
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+ * the memory region pointed at by @data is determined by the
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+ * mailbox provider. Providers that solely transfer notifications
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+ * will ignore this parameter.
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+ * @return 0 if OK, or a negative error code.
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+ */
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+int mbox_send(struct mbox_chan *chan, const void *data);
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+
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+/**
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+ * mbox_recv - Receive any available message from a mailbox channel
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+ *
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+ * This function will wait (up to the specified @timeout_us) for a message to
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+ * be sent by the remote entity, and write the content of any such message
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+ * into a caller-provided buffer.
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+ *
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+ * @chan: A channel object that was previously successfully requested by
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+ * calling mbox_get_by_*().
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+ * @data: A pointer to the buffer to receive the message. The format and
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+ * size of the memory region pointed at by @data is determined by
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+ * the mailbox provider. Providers that solely transfer
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+ * notifications will ignore this parameter.
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+ * @timeout_us: The maximum time to wait for a message to be available, in
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+ * micro-seconds. A value of 0 does not wait at all.
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+ * @return 0 if OK, -ENODATA if no message was available, or a negative error
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+ * code.
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+ */
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+int mbox_recv(struct mbox_chan *chan, void *data, ulong timeout_us);
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+
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+#endif
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