include/drivers/mbox.h

/**
 * @file
 *
 * @brief Generic low-level multi-channel inter-processor mailbox communication API.
 */

/*
 * Copyright (c) 2021 Carlo Caione <ccaione@baylibre.com>
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#ifndef ZEPHYR_INCLUDE_DRIVERS_MBOX_H_
#define ZEPHYR_INCLUDE_DRIVERS_MBOX_H_

/**
 * @brief MBOX Interface
 * @defgroup mbox_interface MBOX Interface
 * @ingroup io_interfaces
 * @{
 *
 * @code{.unparsed}
 *
 *                      CPU #1        |
 * +----------+                       |        +----------+
 * |          +---TX9----+   +--------+--RX8---+          |
 * |  dev A   |          |   |        |        |  CPU #2  |
 * |          <---RX8--+ |   | +------+--TX9--->          |
 * +----------+        | |   | |      |        +----------+
 *                  +--+-v---v-+--+   |
 *                  |             |   |
 *                  |   MBOX dev  |   |
 *                  |             |   |
 *                  +--+-^---^--+-+   |
 * +----------+        | |   |  |     |        +----------+
 * |          <---RX2--+ |   |  +-----+--TX3--->          |
 * |  dev B   |          |   |        |        |  CPU #3  |
 * |          +---TX3----+   +--------+--RX2---+          |
 * +----------+                       |        +----------+
 *                                    |
 *
 * @endcode
 *
 * An MBOX device is a peripheral capable of passing signals (and data depending
 * on the peripheral) between CPUs and clusters in the system. Each MBOX
 * instance is providing one or more channels, each one targeting one other CPU
 * cluster (multiple channels can target the same cluster).
 *
 * For example in the plot the device 'dev A' is using the TX channel 9 to
 * signal (or send data to) the CPU #2 and it's expecting data or signals on
 * the RX channel 8. Thus it can send the message through the channel 9, and it
 * can register a callback on the channel 8 of the MBOX device.
 *
 * This API supports two modes: signalling mode and data transfer mode.
 *
 * In signalling mode:
 *  - mbox_mtu_get() must return 0
 *  - mbox_send() must have (msg == NULL)
 *  - the callback must be called with (data == NULL)
 *
 * In data transfer mode:
 *  - mbox_mtu_get() must return a (value != 0)
 *  - mbox_send() must have (msg != NULL)
 *  - the callback must be called with (data != NULL)
 *  - The msg content must be the same between sender and receiver
 *
 */

#include <kernel.h>
#include <device.h>
#include <devicetree/mbox.h>

#ifdef __cplusplus
extern "C" {
#endif

/**
 * @brief Message struct (to hold data and its size).
 */
struct mbox_msg {
	/** Pointer to the data sent in the message. */
	const void *data;

	/** Size of the data. */
	size_t size;
};

/**
 * @brief Provides a type to hold an MBOX channel
 *
 * Struct type to hold an MBOX device pointer and the channel ID.
 */
struct mbox_channel {
	/** MBOX device pointer. */
	const struct device *dev;

	/** Channel ID. */
	uint32_t id;
};

/**
 * @brief Structure initializer for mbox_channel from devicetree
 *
 * This helper macro expands to a static initializer for a @p mbox_channel by
 * reading the relevant device controller and channel number from the
 * devicetree.
 *
 * Example devicetree fragment:
 *
 *     mbox1: mbox-controller@... { ... };
 *
 *     n: node {
 *             mboxes = <&mbox1 8>,
 *                      <&mbox1 9>;
 *             mbox-names = "tx", "rx";
 *     };
 *
 * Example usage:
 *
 *     const struct mbox_channel channel = MBOX_DT_CHANNEL_GET(DT_NODELABEL(n), tx);
 *
 * @param node_id Devicetree node identifier for the MBOX device
 * @param name lowercase-and-underscores name of the mboxes element
 */
#define MBOX_DT_CHANNEL_GET(node_id, name)					\
	{									\
		.dev = DEVICE_DT_GET(DT_MBOX_CTLR_BY_NAME(node_id, name)),	\
		.id = DT_MBOX_CHANNEL_BY_NAME(node_id, name),			\
	}

/**
 * @typedef mbox_callback_t
 *
 * @brief Callback API for incoming MBOX messages
 *
 * These callbacks execute in interrupt context. Therefore, use only
 * interrupt-safe APIS. Registration of callbacks is done via @a
 * mbox_register_callback()
 *
 * The data parameter must be NULL in signalling mode.
 *
 * @param dev Driver instance
 * @param channel Channel ID
 * @param user_data Pointer to some private data provided at registration
 *        time
 * @param data Message struct
 */
typedef void (*mbox_callback_t)(const struct device *dev, uint32_t channel,
				void *user_data, struct mbox_msg *data);

/**
 * @typedef mbox_send_t
 *
 * @brief Callback API to send MBOX messages
 *
 * See @a mbox_send() for function description
 *
 * @param dev Driver instance
 * @param channel Channel ID
 * @param msg Message struct
 *
 * @return See return values for @a mbox_send()
 */
typedef int (*mbox_send_t)(const struct device *dev, uint32_t channel,
			   const struct mbox_msg *msg);

/**
 * @typedef mbox_mtu_get_t
 *
 * @brief Callback API to get maximum data size
 *
 * See @a mbox_mtu_get() for argument definitions.
 */
typedef int (*mbox_mtu_get_t)(const struct device *dev);

/**
 * @typedef mbox_register_callback_t
 *
 * @brief Callback API upon registration
 *
 * See @a mbox_register_callback() for function description
 *
 * @param dev Driver instance
 * @param channel Channel ID
 * @param cb Callback function to execute on incoming message interrupts.
 * @param user_data Application-specific data pointer which will be passed
 *        to the callback function when executed.
 *
 * @return See return values for @a mbox_register_callback()
 */
typedef int (*mbox_register_callback_t)(const struct device *dev,
					uint32_t channel,
					mbox_callback_t cb,
					void *user_data);

/**
 * @typedef mbox_set_enabled_t
 *
 * @brief Callback API upon enablement of interrupts
 *
 * See @a mbox_set_enabled() for function description
 *
 * @param dev Driver instance
 * @param channel Channel ID
 * @param enable Set to 0 to disable and to nonzero to enable.
 *
 * @return See return values for @a mbox_set_enabled()
 */
typedef int (*mbox_set_enabled_t)(const struct device *dev, uint32_t channel, bool enable);

/**
 * @typedef mbox_max_channels_get_t
 *
 * @brief Callback API to get maximum number of channels
 *
 * See @a mbox_max_channels_get() for argument definitions.
 */
typedef uint32_t (*mbox_max_channels_get_t)(const struct device *dev);

__subsystem struct mbox_driver_api {
	mbox_send_t send;
	mbox_register_callback_t register_callback;
	mbox_mtu_get_t mtu_get;
	mbox_max_channels_get_t max_channels_get;
	mbox_set_enabled_t set_enabled;
};

/**
 * @brief Initialize a channel struct
 *
 * Initialize an @p mbox_channel passed by the user with a provided MBOX device
 * and channel ID. This function is needed when the information about the
 * device and the channel ID is not in the DT. In the DT case
 * MBOX_DT_CHANNEL_GET() must be used instead.
 *
 * @param channel Pointer to the channel struct
 * @param dev Driver instance
 * @param ch_id Channel ID
 */
static inline void mbox_init_channel(struct mbox_channel *channel, const struct device *dev,
				     uint32_t ch_id)
{
	channel->dev = dev;
	channel->id = ch_id;
}

/**
 * @brief Try to send a message over the MBOX device.
 *
 * Send a message over an @p mbox_channel. The msg parameter must be NULL when
 * the driver is used for signalling.
 *
 * If the msg parameter is not NULL, this data is expected to be delivered on
 * the receiving side using the data parameter of the receiving callback.
 *
 * @param channel Channel instance pointer
 * @param msg Pointer to the message struct
 *
 * @retval -EBUSY    If the remote hasn't yet read the last data sent.
 * @retval -EMSGSIZE If the supplied data size is unsupported by the driver.
 * @retval -EINVAL   If there was a bad parameter, such as: too-large channel
 *		     descriptor or the device isn't an outbound MBOX channel.
 *
 * @retval 0         On success, negative value on error.
 */
__syscall int mbox_send(const struct mbox_channel *channel, const struct mbox_msg *msg);

static inline int z_impl_mbox_send(const struct mbox_channel *channel, const struct mbox_msg *msg)
{
	const struct mbox_driver_api *api =
		(const struct mbox_driver_api *)channel->dev->api;

	if (api->send == NULL) {
		return -ENOSYS;
	}

	return api->send(channel->dev, channel->id, msg);
}

/**
 * @brief Register a callback function on a channel for incoming messages.
 *
 * This function doesn't assume anything concerning the status of the
 * interrupts. Use @a mbox_set_enabled() to enable or to disable the interrupts
 * if needed.
 *
 * @param channel Channel instance pointer.
 * @param cb Callback function to execute on incoming message interrupts.
 * @param user_data Application-specific data pointer which will be passed
 *        to the callback function when executed.
 *
 * @retval 0 On success, negative value on error.
 */
static inline int mbox_register_callback(const struct mbox_channel *channel,
					 mbox_callback_t cb,
					 void *user_data)
{
	const struct mbox_driver_api *api =
		(const struct mbox_driver_api *)channel->dev->api;

	if (api->register_callback == NULL) {
		return -ENOSYS;
	}

	return api->register_callback(channel->dev, channel->id, cb, user_data);
}

/**
 * @brief Return the maximum number of bytes possible in an outbound message.
 *
 * Returns the actual number of bytes that it is possible to send through an
 * outgoing channel.
 *
 * This number can be 0 when the driver only supports signalling or when on the
 * receiving side the content and size of the message must be retrieved in an
 * indirect way (i.e. probing some other peripheral, reading memory regions,
 * etc...).
 *
 * If this function returns 0, the msg parameter in @a mbox_send() is expected
 * to be NULL.
 *
 * @param dev Driver instance pointer.
 *
 * @return Maximum possible size of a message in bytes, 0 for signalling,
 *	   negative value on error.
 */
__syscall int mbox_mtu_get(const struct device *dev);

static inline int z_impl_mbox_mtu_get(const struct device *dev)
{
	const struct mbox_driver_api *api =
		(const struct mbox_driver_api *)dev->api;

	if (api->mtu_get == NULL) {
		return -ENOSYS;
	}

	return api->mtu_get(dev);
}

/**
 * @brief Enable (disable) interrupts and callbacks for inbound channels.
 *
 * Enable interrupt for the channel when the parameter 'enable' is set to true.
 * Disable it otherwise.
 *
 * Immediately after calling this function with 'enable' set to true, the
 * channel is considered enabled and ready to receive signal and messages (even
 * already pending), so the user must take care of installing a proper callback
 * (if needed) using @a mbox_register_callback() on the channel before enabling
 * it. For this reason it is recommended that all the channels are disabled at
 * probe time.
 *
 * Enabling a channel for which there is no installed callback is considered
 * undefined behavior (in general the driver must take care of gracefully
 * handling spurious interrupts with no installed callback).
 *
 * @param channel Channel instance pointer.
 * @param enable Set to 0 to disable and to nonzero to enable.
 *
 * @retval 0       On success.
 * @retval -EINVAL If it isn't an inbound channel.
 */
__syscall int mbox_set_enabled(const struct mbox_channel *channel, bool enable);

static inline int z_impl_mbox_set_enabled(const struct mbox_channel *channel, bool enable)
{
	const struct mbox_driver_api *api =
		(const struct mbox_driver_api *)channel->dev->api;

	if (api->set_enabled == NULL) {
		return -ENOSYS;
	}

	return api->set_enabled(channel->dev, channel->id, enable);
}

/**
 * @brief Return the maximum number of channels.
 *
 * Return the maximum number of channels supported by the hardware.
 *
 * @param dev Driver instance pointer.
 *
 * @return Maximum possible number of supported channels on success, negative
 *	   value on error.
 */
__syscall uint32_t mbox_max_channels_get(const struct device *dev);

static inline uint32_t z_impl_mbox_max_channels_get(const struct device *dev)
{
	const struct mbox_driver_api *api =
		(const struct mbox_driver_api *)dev->api;

	if (api->max_channels_get == NULL) {
		return -ENOSYS;
	}

	return api->max_channels_get(dev);
}

#ifdef __cplusplus
}
#endif

/**
 * @}
 */

#include <syscalls/mbox.h>

#endif /* ZEPHYR_INCLUDE_DRIVERS_MBOX_H_ */