mailbox: Introduce framework for mailbox

Introduce common framework for client/protocol drivers and
controller drivers of Inter-Processor-Communication (IPC).

Client driver developers should have a look at
 include/linux/mailbox_client.h to understand the part of
the API exposed to client drivers.
Similarly controller driver developers should have a look
at include/linux/mailbox_controller.h

Reviewed-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>

5 files changed, 656 insertions, 0 deletions

diff --git a/MAINTAINERS b/MAINTAINERS
index a12edf2624e5..c5f7c854b6d2 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -5740,6 +5740,14 @@ S:	Maintained
 F:      drivers/net/macvlan.c
 F:      include/linux/if_macvlan.h
 
+MAILBOX API
+M:      Jassi Brar <jassisinghbrar@gmail.com>
+L:      linux-kernel@vger.kernel.org
+S:      Maintained
+F:      drivers/mailbox/
+F:      include/linux/mailbox_client.h
+F:      include/linux/mailbox_controller.h
+
 MAN-PAGES: MANUAL PAGES FOR LINUX -- Sections 2, 3, 4, 5, and 7
 M:      Michael Kerrisk <mtk.manpages@gmail.com>
 W:      http://www.kernel.org/doc/man-pages
diff --git a/drivers/mailbox/Makefile b/drivers/mailbox/Makefile
index 6d184dbcaca8..94ed7cefb14d 100644
--- a/drivers/mailbox/Makefile
+++ b/drivers/mailbox/Makefile
@@ -1,3 +1,7 @@
+# Generic MAILBOX API
+
+obj-$(CONFIG_MAILBOX)           += mailbox.o
+
 obj-$(CONFIG_PL320_MBOX)        += pl320-ipc.o
 
 obj-$(CONFIG_OMAP2PLUS_MBOX)    += omap-mailbox.o
diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
new file mode 100644
index 000000000000..afcb430508ec
--- /dev/null
+++ b/drivers/mailbox/mailbox.c
@@ -0,0 +1,465 @@
+/*
+ * Mailbox: Common code for Mailbox controllers and users
+ *
+ * Copyright (C) 2013-2014 Linaro Ltd.
+ * Author: Jassi Brar <jassisinghbrar@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/interrupt.h>
+#include <linux/spinlock.h>
+#include <linux/mutex.h>
+#include <linux/delay.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/bitops.h>
+#include <linux/mailbox_client.h>
+#include <linux/mailbox_controller.h>
+
+#define TXDONE_BY_IRQ   BIT(0) /* controller has remote RTR irq */
+#define TXDONE_BY_POLL  BIT(1) /* controller can read status of last TX */
+#define TXDONE_BY_ACK   BIT(2) /* S/W ACK recevied by Client ticks the TX */
+
+static LIST_HEAD(mbox_cons);
+static DEFINE_MUTEX(con_mutex);
+
+static int add_to_rbuf(struct mbox_chan *chan, void *mssg)
+{
+        int idx;
+        unsigned long flags;
+
+        spin_lock_irqsave(&chan->lock, flags);
+
+        /* See if there is any space left */
+        if (chan->msg_count == MBOX_TX_QUEUE_LEN) {
+                spin_unlock_irqrestore(&chan->lock, flags);
+                return -ENOBUFS;
+        }
+
+        idx = chan->msg_free;
+        chan->msg_data[idx] = mssg;
+        chan->msg_count++;
+
+        if (idx == MBOX_TX_QUEUE_LEN - 1)
+                chan->msg_free = 0;
+        else
+                chan->msg_free++;
+
+        spin_unlock_irqrestore(&chan->lock, flags);
+
+        return idx;
+}
+
+static void msg_submit(struct mbox_chan *chan)
+{
+        unsigned count, idx;
+        unsigned long flags;
+        void *data;
+        int err;
+
+        spin_lock_irqsave(&chan->lock, flags);
+
+        if (!chan->msg_count || chan->active_req)
+                goto exit;
+
+        count = chan->msg_count;
+        idx = chan->msg_free;
+        if (idx >= count)
+                idx -= count;
+        else
+                idx += MBOX_TX_QUEUE_LEN - count;
+
+        data = chan->msg_data[idx];
+
+        /* Try to submit a message to the MBOX controller */
+        err = chan->mbox->ops->send_data(chan, data);
+        if (!err) {
+                chan->active_req = data;
+                chan->msg_count--;
+        }
+exit:
+        spin_unlock_irqrestore(&chan->lock, flags);
+}
+
+static void tx_tick(struct mbox_chan *chan, int r)
+{
+        unsigned long flags;
+        void *mssg;
+
+        spin_lock_irqsave(&chan->lock, flags);
+        mssg = chan->active_req;
+        chan->active_req = NULL;
+        spin_unlock_irqrestore(&chan->lock, flags);
+
+        /* Submit next message */
+        msg_submit(chan);
+
+        /* Notify the client */
+        if (mssg && chan->cl->tx_done)
+                chan->cl->tx_done(chan->cl, mssg, r);
+
+        if (chan->cl->tx_block)
+                complete(&chan->tx_complete);
+}
+
+static void poll_txdone(unsigned long data)
+{
+        struct mbox_controller *mbox = (struct mbox_controller *)data;
+        bool txdone, resched = false;
+        int i;
+
+        for (i = 0; i < mbox->num_chans; i++) {
+                struct mbox_chan *chan = &mbox->chans[i];
+
+                if (chan->active_req && chan->cl) {
+                        resched = true;
+                        txdone = chan->mbox->ops->last_tx_done(chan);
+                        if (txdone)
+                                tx_tick(chan, 0);
+                }
+        }
+
+        if (resched)
+                mod_timer(&mbox->poll, jiffies +
+                                msecs_to_jiffies(mbox->txpoll_period));
+}
+
+/**
+ * mbox_chan_received_data - A way for controller driver to push data
+ *                              received from remote to the upper layer.
+ * @chan: Pointer to the mailbox channel on which RX happened.
+ * @mssg: Client specific message typecasted as void *
+ *
+ * After startup and before shutdown any data received on the chan
+ * is passed on to the API via atomic mbox_chan_received_data().
+ * The controller should ACK the RX only after this call returns.
+ */
+void mbox_chan_received_data(struct mbox_chan *chan, void *mssg)
+{
+        /* No buffering the received data */
+        if (chan->cl->rx_callback)
+                chan->cl->rx_callback(chan->cl, mssg);
+}
+EXPORT_SYMBOL_GPL(mbox_chan_received_data);
+
+/**
+ * mbox_chan_txdone - A way for controller driver to notify the
+ *                      framework that the last TX has completed.
+ * @chan: Pointer to the mailbox chan on which TX happened.
+ * @r: Status of last TX - OK or ERROR
+ *
+ * The controller that has IRQ for TX ACK calls this atomic API
+ * to tick the TX state machine. It works only if txdone_irq
+ * is set by the controller.
+ */
+void mbox_chan_txdone(struct mbox_chan *chan, int r)
+{
+        if (unlikely(!(chan->txdone_method & TXDONE_BY_IRQ))) {
+                dev_err(chan->mbox->dev,
+                       "Controller can't run the TX ticker\n");
+                return;
+        }
+
+        tx_tick(chan, r);
+}
+EXPORT_SYMBOL_GPL(mbox_chan_txdone);
+
+/**
+ * mbox_client_txdone - The way for a client to run the TX state machine.
+ * @chan: Mailbox channel assigned to this client.
+ * @r: Success status of last transmission.
+ *
+ * The client/protocol had received some 'ACK' packet and it notifies
+ * the API that the last packet was sent successfully. This only works
+ * if the controller can't sense TX-Done.
+ */
+void mbox_client_txdone(struct mbox_chan *chan, int r)
+{
+        if (unlikely(!(chan->txdone_method & TXDONE_BY_ACK))) {
+                dev_err(chan->mbox->dev, "Client can't run the TX ticker\n");
+                return;
+        }
+
+        tx_tick(chan, r);
+}
+EXPORT_SYMBOL_GPL(mbox_client_txdone);
+
+/**
+ * mbox_client_peek_data - A way for client driver to pull data
+ *                      received from remote by the controller.
+ * @chan: Mailbox channel assigned to this client.
+ *
+ * A poke to controller driver for any received data.
+ * The data is actually passed onto client via the
+ * mbox_chan_received_data()
+ * The call can be made from atomic context, so the controller's
+ * implementation of peek_data() must not sleep.
+ *
+ * Return: True, if controller has, and is going to push after this,
+ *          some data.
+ *         False, if controller doesn't have any data to be read.
+ */
+bool mbox_client_peek_data(struct mbox_chan *chan)
+{
+        if (chan->mbox->ops->peek_data)
+                return chan->mbox->ops->peek_data(chan);
+
+        return false;
+}
+EXPORT_SYMBOL_GPL(mbox_client_peek_data);
+
+/**
+ * mbox_send_message -  For client to submit a message to be
+ *                              sent to the remote.
+ * @chan: Mailbox channel assigned to this client.
+ * @mssg: Client specific message typecasted.
+ *
+ * For client to submit data to the controller destined for a remote
+ * processor. If the client had set 'tx_block', the call will return
+ * either when the remote receives the data or when 'tx_tout' millisecs
+ * run out.
+ *  In non-blocking mode, the requests are buffered by the API and a
+ * non-negative token is returned for each queued request. If the request
+ * is not queued, a negative token is returned. Upon failure or successful
+ * TX, the API calls 'tx_done' from atomic context, from which the client
+ * could submit yet another request.
+ * The pointer to message should be preserved until it is sent
+ * over the chan, i.e, tx_done() is made.
+ * This function could be called from atomic context as it simply
+ * queues the data and returns a token against the request.
+ *
+ * Return: Non-negative integer for successful submission (non-blocking mode)
+ *      or transmission over chan (blocking mode).
+ *      Negative value denotes failure.
+ */
+int mbox_send_message(struct mbox_chan *chan, void *mssg)
+{
+        int t;
+
+        if (!chan || !chan->cl)
+                return -EINVAL;
+
+        t = add_to_rbuf(chan, mssg);
+        if (t < 0) {
+                dev_err(chan->mbox->dev, "Try increasing MBOX_TX_QUEUE_LEN\n");
+                return t;
+        }
+
+        msg_submit(chan);
+
+        if (chan->txdone_method == TXDONE_BY_POLL)
+                poll_txdone((unsigned long)chan->mbox);
+
+        if (chan->cl->tx_block && chan->active_req) {
+                unsigned long wait;
+                int ret;
+
+                if (!chan->cl->tx_tout) /* wait forever */
+                        wait = msecs_to_jiffies(3600000);
+                else
+                        wait = msecs_to_jiffies(chan->cl->tx_tout);
+
+                ret = wait_for_completion_timeout(&chan->tx_complete, wait);
+                if (ret == 0) {
+                        t = -EIO;
+                        tx_tick(chan, -EIO);
+                }
+        }
+
+        return t;
+}
+EXPORT_SYMBOL_GPL(mbox_send_message);
+
+/**
+ * mbox_request_channel - Request a mailbox channel.
+ * @cl: Identity of the client requesting the channel.
+ * @index: Index of mailbox specifier in 'mboxes' property.
+ *
+ * The Client specifies its requirements and capabilities while asking for
+ * a mailbox channel. It can't be called from atomic context.
+ * The channel is exclusively allocated and can't be used by another
+ * client before the owner calls mbox_free_channel.
+ * After assignment, any packet received on this channel will be
+ * handed over to the client via the 'rx_callback'.
+ * The framework holds reference to the client, so the mbox_client
+ * structure shouldn't be modified until the mbox_free_channel returns.
+ *
+ * Return: Pointer to the channel assigned to the client if successful.
+ *              ERR_PTR for request failure.
+ */
+struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index)
+{
+        struct device *dev = cl->dev;
+        struct mbox_controller *mbox;
+        struct of_phandle_args spec;
+        struct mbox_chan *chan;
+        unsigned long flags;
+        int ret;
+
+        if (!dev || !dev->of_node) {
+                pr_debug("%s: No owner device node\n", __func__);
+                return ERR_PTR(-ENODEV);
+        }
+
+        mutex_lock(&con_mutex);
+
+        if (of_parse_phandle_with_args(dev->of_node, "mboxes",
+                                       "#mbox-cells", index, &spec)) {
+                dev_dbg(dev, "%s: can't parse \"mboxes\" property\n", __func__);
+                mutex_unlock(&con_mutex);
+                return ERR_PTR(-ENODEV);
+        }
+
+        chan = NULL;
+        list_for_each_entry(mbox, &mbox_cons, node)
+                if (mbox->dev->of_node == spec.np) {
+                        chan = mbox->of_xlate(mbox, &spec);
+                        break;
+                }
+
+        of_node_put(spec.np);
+
+        if (!chan || chan->cl || !try_module_get(mbox->dev->driver->owner)) {
+                dev_dbg(dev, "%s: mailbox not free\n", __func__);
+                mutex_unlock(&con_mutex);
+                return ERR_PTR(-EBUSY);
+        }
+
+        spin_lock_irqsave(&chan->lock, flags);
+        chan->msg_free = 0;
+        chan->msg_count = 0;
+        chan->active_req = NULL;
+        chan->cl = cl;
+        init_completion(&chan->tx_complete);
+
+        if (chan->txdone_method == TXDONE_BY_POLL && cl->knows_txdone)
+                chan->txdone_method |= TXDONE_BY_ACK;
+
+        spin_unlock_irqrestore(&chan->lock, flags);
+
+        ret = chan->mbox->ops->startup(chan);
+        if (ret) {
+                dev_err(dev, "Unable to startup the chan (%d)\n", ret);
+                mbox_free_channel(chan);
+                chan = ERR_PTR(ret);
+        }
+
+        mutex_unlock(&con_mutex);
+        return chan;
+}
+EXPORT_SYMBOL_GPL(mbox_request_channel);
+
+/**
+ * mbox_free_channel - The client relinquishes control of a mailbox
+ *                      channel by this call.
+ * @chan: The mailbox channel to be freed.
+ */
+void mbox_free_channel(struct mbox_chan *chan)
+{
+        unsigned long flags;
+
+        if (!chan || !chan->cl)
+                return;
+
+        chan->mbox->ops->shutdown(chan);
+
+        /* The queued TX requests are simply aborted, no callbacks are made */
+        spin_lock_irqsave(&chan->lock, flags);
+        chan->cl = NULL;
+        chan->active_req = NULL;
+        if (chan->txdone_method == (TXDONE_BY_POLL | TXDONE_BY_ACK))
+                chan->txdone_method = TXDONE_BY_POLL;
+
+        module_put(chan->mbox->dev->driver->owner);
+        spin_unlock_irqrestore(&chan->lock, flags);
+}
+EXPORT_SYMBOL_GPL(mbox_free_channel);
+
+static struct mbox_chan *
+of_mbox_index_xlate(struct mbox_controller *mbox,
+                    const struct of_phandle_args *sp)
+{
+        int ind = sp->args[0];
+
+        if (ind >= mbox->num_chans)
+                return NULL;
+
+        return &mbox->chans[ind];
+}
+
+/**
+ * mbox_controller_register - Register the mailbox controller
+ * @mbox:       Pointer to the mailbox controller.
+ *
+ * The controller driver registers its communication channels
+ */
+int mbox_controller_register(struct mbox_controller *mbox)
+{
+        int i, txdone;
+
+        /* Sanity check */
+        if (!mbox || !mbox->dev || !mbox->ops || !mbox->num_chans)
+                return -EINVAL;
+
+        if (mbox->txdone_irq)
+                txdone = TXDONE_BY_IRQ;
+        else if (mbox->txdone_poll)
+                txdone = TXDONE_BY_POLL;
+        else /* It has to be ACK then */
+                txdone = TXDONE_BY_ACK;
+
+        if (txdone == TXDONE_BY_POLL) {
+                mbox->poll.function = &poll_txdone;
+                mbox->poll.data = (unsigned long)mbox;
+                init_timer(&mbox->poll);
+        }
+
+        for (i = 0; i < mbox->num_chans; i++) {
+                struct mbox_chan *chan = &mbox->chans[i];
+
+                chan->cl = NULL;
+                chan->mbox = mbox;
+                chan->txdone_method = txdone;
+                spin_lock_init(&chan->lock);
+        }
+
+        if (!mbox->of_xlate)
+                mbox->of_xlate = of_mbox_index_xlate;
+
+        mutex_lock(&con_mutex);
+        list_add_tail(&mbox->node, &mbox_cons);
+        mutex_unlock(&con_mutex);
+
+        return 0;
+}
+EXPORT_SYMBOL_GPL(mbox_controller_register);
+
+/**
+ * mbox_controller_unregister - Unregister the mailbox controller
+ * @mbox:       Pointer to the mailbox controller.
+ */
+void mbox_controller_unregister(struct mbox_controller *mbox)
+{
+        int i;
+
+        if (!mbox)
+                return;
+
+        mutex_lock(&con_mutex);
+
+        list_del(&mbox->node);
+
+        for (i = 0; i < mbox->num_chans; i++)
+                mbox_free_channel(&mbox->chans[i]);
+
+        if (mbox->txdone_poll)
+                del_timer_sync(&mbox->poll);
+
+        mutex_unlock(&con_mutex);
+}
+EXPORT_SYMBOL_GPL(mbox_controller_unregister);
diff --git a/include/linux/mailbox_client.h b/include/linux/mailbox_client.h
new file mode 100644
index 000000000000..307d9cab2026
--- /dev/null
+++ b/include/linux/mailbox_client.h
@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2013-2014 Linaro Ltd.
+ * Author: Jassi Brar <jassisinghbrar@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef __MAILBOX_CLIENT_H
+#define __MAILBOX_CLIENT_H
+
+#include <linux/of.h>
+#include <linux/device.h>
+
+struct mbox_chan;
+
+/**
+ * struct mbox_client - User of a mailbox
+ * @dev:                The client device
+ * @tx_block:           If the mbox_send_message should block until data is
+ *                      transmitted.
+ * @tx_tout:            Max block period in ms before TX is assumed failure
+ * @knows_txdone:       If the client could run the TX state machine. Usually
+ *                      if the client receives some ACK packet for transmission.
+ *                      Unused if the controller already has TX_Done/RTR IRQ.
+ * @rx_callback:        Atomic callback to provide client the data received
+ * @tx_done:            Atomic callback to tell client of data transmission
+ */
+struct mbox_client {
+        struct device *dev;
+        bool tx_block;
+        unsigned long tx_tout;
+        bool knows_txdone;
+
+        void (*rx_callback)(struct mbox_client *cl, void *mssg);
+        void (*tx_done)(struct mbox_client *cl, void *mssg, int r);
+};
+
+struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index);
+int mbox_send_message(struct mbox_chan *chan, void *mssg);
+void mbox_client_txdone(struct mbox_chan *chan, int r); /* atomic */
+bool mbox_client_peek_data(struct mbox_chan *chan); /* atomic */
+void mbox_free_channel(struct mbox_chan *chan); /* may sleep */
+
+#endif /* __MAILBOX_CLIENT_H */
diff --git a/include/linux/mailbox_controller.h b/include/linux/mailbox_controller.h
new file mode 100644
index 000000000000..d4cf96f07cfc
--- /dev/null
+++ b/include/linux/mailbox_controller.h
@@ -0,0 +1,133 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef __MAILBOX_CONTROLLER_H
+#define __MAILBOX_CONTROLLER_H
+
+#include <linux/of.h>
+#include <linux/types.h>
+#include <linux/timer.h>
+#include <linux/device.h>
+#include <linux/completion.h>
+
+struct mbox_chan;
+
+/**
+ * struct mbox_chan_ops - methods to control mailbox channels
+ * @send_data:  The API asks the MBOX controller driver, in atomic
+ *              context try to transmit a message on the bus. Returns 0 if
+ *              data is accepted for transmission, -EBUSY while rejecting
+ *              if the remote hasn't yet read the last data sent. Actual
+ *              transmission of data is reported by the controller via
+ *              mbox_chan_txdone (if it has some TX ACK irq). It must not
+ *              sleep.
+ * @startup:    Called when a client requests the chan. The controller
+ *              could ask clients for additional parameters of communication
+ *              to be provided via client's chan_data. This call may
+ *              block. After this call the Controller must forward any
+ *              data received on the chan by calling mbox_chan_received_data.
+ *              The controller may do stuff that need to sleep.
+ * @shutdown:   Called when a client relinquishes control of a chan.
+ *              This call may block too. The controller must not forward
+ *              any received data anymore.
+ *              The controller may do stuff that need to sleep.
+ * @last_tx_done: If the controller sets 'txdone_poll', the API calls
+ *                this to poll status of last TX. The controller must
+ *                give priority to IRQ method over polling and never
+ *                set both txdone_poll and txdone_irq. Only in polling
+ *                mode 'send_data' is expected to return -EBUSY.
+ *                The controller may do stuff that need to sleep/block.
+ *                Used only if txdone_poll:=true && txdone_irq:=false
+ * @peek_data: Atomic check for any received data. Return true if controller
+ *                has some data to push to the client. False otherwise.
+ */
+struct mbox_chan_ops {
+        int (*send_data)(struct mbox_chan *chan, void *data);
+        int (*startup)(struct mbox_chan *chan);
+        void (*shutdown)(struct mbox_chan *chan);
+        bool (*last_tx_done)(struct mbox_chan *chan);
+        bool (*peek_data)(struct mbox_chan *chan);
+};
+
+/**
+ * struct mbox_controller - Controller of a class of communication channels
+ * @dev:                Device backing this controller
+ * @ops:                Operators that work on each communication chan
+ * @chans:              Array of channels
+ * @num_chans:          Number of channels in the 'chans' array.
+ * @txdone_irq:         Indicates if the controller can report to API when
+ *                      the last transmitted data was read by the remote.
+ *                      Eg, if it has some TX ACK irq.
+ * @txdone_poll:        If the controller can read but not report the TX
+ *                      done. Ex, some register shows the TX status but
+ *                      no interrupt rises. Ignored if 'txdone_irq' is set.
+ * @txpoll_period:      If 'txdone_poll' is in effect, the API polls for
+ *                      last TX's status after these many millisecs
+ * @of_xlate:           Controller driver specific mapping of channel via DT
+ * @poll:               API private. Used to poll for TXDONE on all channels.
+ * @node:               API private. To hook into list of controllers.
+ */
+struct mbox_controller {
+        struct device *dev;
+        struct mbox_chan_ops *ops;
+        struct mbox_chan *chans;
+        int num_chans;
+        bool txdone_irq;
+        bool txdone_poll;
+        unsigned txpoll_period;
+        struct mbox_chan *(*of_xlate)(struct mbox_controller *mbox,
+                                      const struct of_phandle_args *sp);
+        /* Internal to API */
+        struct timer_list poll;
+        struct list_head node;
+};
+
+/*
+ * The length of circular buffer for queuing messages from a client.
+ * 'msg_count' tracks the number of buffered messages while 'msg_free'
+ * is the index where the next message would be buffered.
+ * We shouldn't need it too big because every transfer is interrupt
+ * triggered and if we have lots of data to transfer, the interrupt
+ * latencies are going to be the bottleneck, not the buffer length.
+ * Besides, mbox_send_message could be called from atomic context and
+ * the client could also queue another message from the notifier 'tx_done'
+ * of the last transfer done.
+ * REVISIT: If too many platforms see the "Try increasing MBOX_TX_QUEUE_LEN"
+ * print, it needs to be taken from config option or somesuch.
+ */
+#define MBOX_TX_QUEUE_LEN       20
+
+/**
+ * struct mbox_chan - s/w representation of a communication chan
+ * @mbox:               Pointer to the parent/provider of this channel
+ * @txdone_method:      Way to detect TXDone chosen by the API
+ * @cl:                 Pointer to the current owner of this channel
+ * @tx_complete:        Transmission completion
+ * @active_req:         Currently active request hook
+ * @msg_count:          No. of mssg currently queued
+ * @msg_free:           Index of next available mssg slot
+ * @msg_data:           Hook for data packet
+ * @lock:               Serialise access to the channel
+ * @con_priv:           Hook for controller driver to attach private data
+ */
+struct mbox_chan {
+        struct mbox_controller *mbox;
+        unsigned txdone_method;
+        struct mbox_client *cl;
+        struct completion tx_complete;
+        void *active_req;
+        unsigned msg_count, msg_free;
+        void *msg_data[MBOX_TX_QUEUE_LEN];
+        spinlock_t lock; /* Serialise access to the channel */
+        void *con_priv;
+};
+
+int mbox_controller_register(struct mbox_controller *mbox); /* can sleep */
+void mbox_controller_unregister(struct mbox_controller *mbox); /* can sleep */
+void mbox_chan_received_data(struct mbox_chan *chan, void *data); /* atomic */
+void mbox_chan_txdone(struct mbox_chan *chan, int r); /* atomic */
+
+#endif /* __MAILBOX_CONTROLLER_H */