[v13,05/24] mailbox: Add Gunyah message queue mailbox

Gunyah message queues are a unidirectional inter-VM pipe for messages up
to 1024 bytes. This driver supports pairing a receiver message queue and
a transmitter message queue to expose a single mailbox channel.

Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
---
 Documentation/virt/gunyah/message-queue.rst |   8 +
 drivers/mailbox/Makefile                    |   2 +
 drivers/mailbox/gunyah-msgq.c               | 212 ++++++++++++++++++++
 include/linux/gunyah.h                      |  57 ++++++
 4 files changed, 279 insertions(+)
 create mode 100644 drivers/mailbox/gunyah-msgq.c

On 09/05/2023 23:47, Elliot Berman wrote:
> Gunyah message queues are a unidirectional inter-VM pipe for messages up
> to 1024 bytes. This driver supports pairing a receiver message queue and
> a transmitter message queue to expose a single mailbox channel.
> 
> Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
> ---
>   Documentation/virt/gunyah/message-queue.rst |   8 +
>   drivers/mailbox/Makefile                    |   2 +
>   drivers/mailbox/gunyah-msgq.c               | 212 ++++++++++++++++++++
>   include/linux/gunyah.h                      |  57 ++++++
>   4 files changed, 279 insertions(+)
>   create mode 100644 drivers/mailbox/gunyah-msgq.c
> 
> diff --git a/Documentation/virt/gunyah/message-queue.rst b/Documentation/virt/gunyah/message-queue.rst
> index b352918ae54b..70d82a4ef32d 100644
> --- a/Documentation/virt/gunyah/message-queue.rst
> +++ b/Documentation/virt/gunyah/message-queue.rst

Note, this file is not a part of the patchset. Trying to apply the 
patchset results in rejects. Probably you missed the documentation patch 
when sending this series.

> @@ -61,3 +61,11 @@ vIRQ: two TX message queues will have two vIRQs (and two capability IDs).
>         |               |         |                 |         |               |
>         |               |         |                 |         |               |
>         +---------------+         +-----------------+         +---------------+
> +
> +Gunyah message queues are exposed as mailboxes. To create the mailbox, create
> +a mbox_client and call `gh_msgq_init()`. On receipt of the RX_READY interrupt,
> +all messages in the RX message queue are read and pushed via the `rx_callback`
> +of the registered mbox_client.
> +
> +.. kernel-doc:: drivers/mailbox/gunyah-msgq.c
> +   :identifiers: gh_msgq_init-- 
With best wishes
Dmitry

On 5/9/23 3:47 PM, Elliot Berman wrote:
> Gunyah message queues are a unidirectional inter-VM pipe for messages up
> to 1024 bytes. This driver supports pairing a receiver message queue and
> a transmitter message queue to expose a single mailbox channel.
> 
> Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>

This patch does not apply properly, because it updates
"message-queue.rst", which does not currently exist.
I'm going to ignore that for now, though.

I'm generally OK with giving you my "Reviewed-by" on this
but I'll wait until you send v14 with the full content
of "message-queue.rst".

Also, I suggest below that you update all your SPDX tags
to no longer use the deprecated "GPL-2.0" identifier.

					-Alex

> ---
>   Documentation/virt/gunyah/message-queue.rst |   8 +
>   drivers/mailbox/Makefile                    |   2 +
>   drivers/mailbox/gunyah-msgq.c               | 212 ++++++++++++++++++++
>   include/linux/gunyah.h                      |  57 ++++++
>   4 files changed, 279 insertions(+)
>   create mode 100644 drivers/mailbox/gunyah-msgq.c
> 
> diff --git a/Documentation/virt/gunyah/message-queue.rst b/Documentation/virt/gunyah/message-queue.rst
> index b352918ae54b..70d82a4ef32d 100644
> --- a/Documentation/virt/gunyah/message-queue.rst
> +++ b/Documentation/virt/gunyah/message-queue.rst
> @@ -61,3 +61,11 @@ vIRQ: two TX message queues will have two vIRQs (and two capability IDs).
>         |               |         |                 |         |               |
>         |               |         |                 |         |               |
>         +---------------+         +-----------------+         +---------------+
> +
> +Gunyah message queues are exposed as mailboxes. To create the mailbox, create
> +a mbox_client and call `gh_msgq_init()`. On receipt of the RX_READY interrupt,
> +all messages in the RX message queue are read and pushed via the `rx_callback`
> +of the registered mbox_client.
> +
> +.. kernel-doc:: drivers/mailbox/gunyah-msgq.c
> +   :identifiers: gh_msgq_init
> diff --git a/drivers/mailbox/Makefile b/drivers/mailbox/Makefile
> index fc9376117111..5f929bb55e9a 100644
> --- a/drivers/mailbox/Makefile
> +++ b/drivers/mailbox/Makefile
> @@ -55,6 +55,8 @@ obj-$(CONFIG_MTK_CMDQ_MBOX)	+= mtk-cmdq-mailbox.o
>   
>   obj-$(CONFIG_ZYNQMP_IPI_MBOX)	+= zynqmp-ipi-mailbox.o
>   
> +obj-$(CONFIG_GUNYAH)		+= gunyah-msgq.o
> +
>   obj-$(CONFIG_SUN6I_MSGBOX)	+= sun6i-msgbox.o
>   
>   obj-$(CONFIG_SPRD_MBOX)		+= sprd-mailbox.o
> diff --git a/drivers/mailbox/gunyah-msgq.c b/drivers/mailbox/gunyah-msgq.c
> new file mode 100644
> index 000000000000..b7a54f233680
> --- /dev/null
> +++ b/drivers/mailbox/gunyah-msgq.c
> @@ -0,0 +1,212 @@
> +// SPDX-License-Identifier: GPL-2.0-only

After seeing this tag I looked into it, and see that SPDX
has deprecated "GPL-2.0" in favor of "GPL-2.0-only".

Please update all SPDX licenses that use "GPL-2.0" to use
this new tag instead.

> +/*
> + * Copyright (c) 2022-2023 Qualcomm Innovation Center, Inc. All rights reserved.
> + */
> +
> +#include <linux/mailbox_controller.h>
> +#include <linux/module.h>
> +#include <linux/interrupt.h>
> +#include <linux/gunyah.h>
> +#include <linux/printk.h>
> +#include <linux/init.h>
> +#include <linux/slab.h>
> +#include <linux/wait.h>
> +
> +#define mbox_chan_to_msgq(chan) (container_of(chan->mbox, struct gh_msgq, mbox))

Parentheses are not needed around a container_of() call.

> +
> +static irqreturn_t gh_msgq_rx_irq_handler(int irq, void *data)
> +{
> +	struct gh_msgq *msgq = data;
> +	struct gh_msgq_rx_data rx_data;
> +	enum gh_error gh_error;
> +	bool ready = true;
> +
> +	while (ready) {
> +		gh_error = gh_hypercall_msgq_recv(msgq->rx_ghrsc->capid,
> +				&rx_data.data, sizeof(rx_data.data),
> +				&rx_data.length, &ready);
> +		if (gh_error != GH_ERROR_OK) {
> +			if (gh_error != GH_ERROR_MSGQUEUE_EMPTY)
> +				dev_warn(msgq->mbox.dev, "Failed to receive data: %d\n", gh_error);
> +			break;
> +		}
> +		if (likely(gh_msgq_chan(msgq)->cl))
> +			mbox_chan_received_data(gh_msgq_chan(msgq), &rx_data);
> +	}
> +
> +	return IRQ_HANDLED;
> +}
> +
> +/* Fired when message queue transitions from "full" to "space available" to send messages */
> +static irqreturn_t gh_msgq_tx_irq_handler(int irq, void *data)
> +{
> +	struct gh_msgq *msgq = data;
> +
> +	mbox_chan_txdone(gh_msgq_chan(msgq), 0);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +/* Fired after sending message and hypercall told us there was more space available. */
> +static void gh_msgq_txdone_tasklet(struct tasklet_struct *tasklet)
> +{
> +	struct gh_msgq *msgq = container_of(tasklet, struct gh_msgq, txdone_tasklet);
> +
> +	mbox_chan_txdone(gh_msgq_chan(msgq), msgq->last_ret);
> +}
> +
> +static int gh_msgq_send_data(struct mbox_chan *chan, void *data)
> +{
> +	struct gh_msgq *msgq = mbox_chan_to_msgq(chan);
> +	struct gh_msgq_tx_data *msgq_data = data;
> +	u64 tx_flags = 0;
> +	enum gh_error gh_error;
> +	bool ready;
> +
> +	if (!msgq->tx_ghrsc)
> +		return -EOPNOTSUPP;
> +
> +	if (msgq_data->push)
> +		tx_flags |= GH_HYPERCALL_MSGQ_TX_FLAGS_PUSH;
> +
> +	gh_error = gh_hypercall_msgq_send(msgq->tx_ghrsc->capid, msgq_data->length, msgq_data->data,
> +						tx_flags, &ready);
> +
> +	/**
> +	 * unlikely because Linux tracks state of msgq and should not try to
> +	 * send message when msgq is full.
> +	 */
> +	if (unlikely(gh_error == GH_ERROR_MSGQUEUE_FULL))
> +		return -EAGAIN;
> +
> +	/**
> +	 * Propagate all other errors to client. If we return error to mailbox
> +	 * framework, then no other messages can be sent and nobody will know
> +	 * to retry this message.
> +	 */
> +	msgq->last_ret = gh_error_remap(gh_error);
> +
> +	/**
> +	 * This message was successfully sent, but message queue isn't ready to
> +	 * accept more messages because it's now full. Mailbox framework
> +	 * requires that we only report that message was transmitted when
> +	 * we're ready to transmit another message. We'll get that in the form
> +	 * of tx IRQ once the other side starts to drain the msgq.
> +	 */
> +	if (gh_error == GH_ERROR_OK) {
> +		if (!ready)
> +			return 0;
> +	} else

Standard style would add curly braces to the else block.

	} else {

> +		dev_err(msgq->mbox.dev, "Failed to send data: %d (%d)\n", gh_error, msgq->last_ret);
> +
> +	/**
> +	 * We can send more messages. Mailbox framework requires that tx done
> +	 * happens asynchronously to sending the message. Gunyah message queues
> +	 * tell us right away on the hypercall return whether we can send more
> +	 * messages. To work around this, defer the txdone to a tasklet.
> +	 */
> +	tasklet_schedule(&msgq->txdone_tasklet);
> +
> +	return 0;
> +}

. . .

On 09/05/2023 21:47, Elliot Berman wrote:
> Gunyah message queues are a unidirectional inter-VM pipe for messages up
> to 1024 bytes. This driver supports pairing a receiver message queue and
> a transmitter message queue to expose a single mailbox channel.
> 
> Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
> ---


Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>

--srini

>   Documentation/virt/gunyah/message-queue.rst |   8 +
>   drivers/mailbox/Makefile                    |   2 +
>   drivers/mailbox/gunyah-msgq.c               | 212 ++++++++++++++++++++
>   include/linux/gunyah.h                      |  57 ++++++
>   4 files changed, 279 insertions(+)
>   create mode 100644 drivers/mailbox/gunyah-msgq.c
> 
> diff --git a/Documentation/virt/gunyah/message-queue.rst b/Documentation/virt/gunyah/message-queue.rst
> index b352918ae54b..70d82a4ef32d 100644
> --- a/Documentation/virt/gunyah/message-queue.rst
> +++ b/Documentation/virt/gunyah/message-queue.rst
> @@ -61,3 +61,11 @@ vIRQ: two TX message queues will have two vIRQs (and two capability IDs).
>         |               |         |                 |         |               |
>         |               |         |                 |         |               |
>         +---------------+         +-----------------+         +---------------+
> +
> +Gunyah message queues are exposed as mailboxes. To create the mailbox, create
> +a mbox_client and call `gh_msgq_init()`. On receipt of the RX_READY interrupt,
> +all messages in the RX message queue are read and pushed via the `rx_callback`
> +of the registered mbox_client.
> +
> +.. kernel-doc:: drivers/mailbox/gunyah-msgq.c
> +   :identifiers: gh_msgq_init
> diff --git a/drivers/mailbox/Makefile b/drivers/mailbox/Makefile
> index fc9376117111..5f929bb55e9a 100644
> --- a/drivers/mailbox/Makefile
> +++ b/drivers/mailbox/Makefile
> @@ -55,6 +55,8 @@ obj-$(CONFIG_MTK_CMDQ_MBOX)	+= mtk-cmdq-mailbox.o
>   
>   obj-$(CONFIG_ZYNQMP_IPI_MBOX)	+= zynqmp-ipi-mailbox.o
>   
> +obj-$(CONFIG_GUNYAH)		+= gunyah-msgq.o
> +
>   obj-$(CONFIG_SUN6I_MSGBOX)	+= sun6i-msgbox.o
>   
>   obj-$(CONFIG_SPRD_MBOX)		+= sprd-mailbox.o
> diff --git a/drivers/mailbox/gunyah-msgq.c b/drivers/mailbox/gunyah-msgq.c
> new file mode 100644
> index 000000000000..b7a54f233680
> --- /dev/null
> +++ b/drivers/mailbox/gunyah-msgq.c
> @@ -0,0 +1,212 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2022-2023 Qualcomm Innovation Center, Inc. All rights reserved.
> + */
> +
> +#include <linux/mailbox_controller.h>
> +#include <linux/module.h>
> +#include <linux/interrupt.h>
> +#include <linux/gunyah.h>
> +#include <linux/printk.h>
> +#include <linux/init.h>
> +#include <linux/slab.h>
> +#include <linux/wait.h>
> +
> +#define mbox_chan_to_msgq(chan) (container_of(chan->mbox, struct gh_msgq, mbox))
> +
> +static irqreturn_t gh_msgq_rx_irq_handler(int irq, void *data)
> +{
> +	struct gh_msgq *msgq = data;
> +	struct gh_msgq_rx_data rx_data;
> +	enum gh_error gh_error;
> +	bool ready = true;
> +
> +	while (ready) {
> +		gh_error = gh_hypercall_msgq_recv(msgq->rx_ghrsc->capid,
> +				&rx_data.data, sizeof(rx_data.data),
> +				&rx_data.length, &ready);
> +		if (gh_error != GH_ERROR_OK) {
> +			if (gh_error != GH_ERROR_MSGQUEUE_EMPTY)
> +				dev_warn(msgq->mbox.dev, "Failed to receive data: %d\n", gh_error);
> +			break;
> +		}
> +		if (likely(gh_msgq_chan(msgq)->cl))
> +			mbox_chan_received_data(gh_msgq_chan(msgq), &rx_data);
> +	}
> +
> +	return IRQ_HANDLED;
> +}
> +
> +/* Fired when message queue transitions from "full" to "space available" to send messages */
> +static irqreturn_t gh_msgq_tx_irq_handler(int irq, void *data)
> +{
> +	struct gh_msgq *msgq = data;
> +
> +	mbox_chan_txdone(gh_msgq_chan(msgq), 0);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +/* Fired after sending message and hypercall told us there was more space available. */
> +static void gh_msgq_txdone_tasklet(struct tasklet_struct *tasklet)
> +{
> +	struct gh_msgq *msgq = container_of(tasklet, struct gh_msgq, txdone_tasklet);
> +
> +	mbox_chan_txdone(gh_msgq_chan(msgq), msgq->last_ret);
> +}
> +
> +static int gh_msgq_send_data(struct mbox_chan *chan, void *data)
> +{
> +	struct gh_msgq *msgq = mbox_chan_to_msgq(chan);
> +	struct gh_msgq_tx_data *msgq_data = data;
> +	u64 tx_flags = 0;
> +	enum gh_error gh_error;
> +	bool ready;
> +
> +	if (!msgq->tx_ghrsc)
> +		return -EOPNOTSUPP;
> +
> +	if (msgq_data->push)
> +		tx_flags |= GH_HYPERCALL_MSGQ_TX_FLAGS_PUSH;
> +
> +	gh_error = gh_hypercall_msgq_send(msgq->tx_ghrsc->capid, msgq_data->length, msgq_data->data,
> +						tx_flags, &ready);
> +
> +	/**
> +	 * unlikely because Linux tracks state of msgq and should not try to
> +	 * send message when msgq is full.
> +	 */
> +	if (unlikely(gh_error == GH_ERROR_MSGQUEUE_FULL))
> +		return -EAGAIN;
> +
> +	/**
> +	 * Propagate all other errors to client. If we return error to mailbox
> +	 * framework, then no other messages can be sent and nobody will know
> +	 * to retry this message.
> +	 */
> +	msgq->last_ret = gh_error_remap(gh_error);
> +
> +	/**
> +	 * This message was successfully sent, but message queue isn't ready to
> +	 * accept more messages because it's now full. Mailbox framework
> +	 * requires that we only report that message was transmitted when
> +	 * we're ready to transmit another message. We'll get that in the form
> +	 * of tx IRQ once the other side starts to drain the msgq.
> +	 */
> +	if (gh_error == GH_ERROR_OK) {
> +		if (!ready)
> +			return 0;
> +	} else
> +		dev_err(msgq->mbox.dev, "Failed to send data: %d (%d)\n", gh_error, msgq->last_ret);
> +
> +	/**
> +	 * We can send more messages. Mailbox framework requires that tx done
> +	 * happens asynchronously to sending the message. Gunyah message queues
> +	 * tell us right away on the hypercall return whether we can send more
> +	 * messages. To work around this, defer the txdone to a tasklet.
> +	 */
> +	tasklet_schedule(&msgq->txdone_tasklet);
> +
> +	return 0;
> +}
> +
> +static struct mbox_chan_ops gh_msgq_ops = {
> +	.send_data = gh_msgq_send_data,
> +};
> +
> +/**
> + * gh_msgq_init() - Initialize a Gunyah message queue with an mbox_client
> + * @parent: device parent used for the mailbox controller
> + * @msgq: Pointer to the gh_msgq to initialize
> + * @cl: A mailbox client to bind to the mailbox channel that the message queue creates
> + * @tx_ghrsc: optional, the transmission side of the message queue
> + * @rx_ghrsc: optional, the receiving side of the message queue
> + *
> + * At least one of tx_ghrsc and rx_ghrsc must be not NULL. Most message queue use cases come with
> + * a pair of message queues to facilitate bidirectional communication. When tx_ghrsc is set,
> + * the client can send messages with mbox_send_message(gh_msgq_chan(msgq), msg). When rx_ghrsc
> + * is set, the mbox_client must register an .rx_callback() and the message queue driver will
> + * deliver all available messages upon receiving the RX ready interrupt. The messages should be
> + * consumed or copied by the client right away as the gh_msgq_rx_data will be replaced/destroyed
> + * after the callback.
> + *
> + * Returns - 0 on success, negative otherwise
> + */
> +int gh_msgq_init(struct device *parent, struct gh_msgq *msgq, struct mbox_client *cl,
> +		 struct gh_resource *tx_ghrsc, struct gh_resource *rx_ghrsc)
> +{
> +	int ret;
> +
> +	/* Must have at least a tx_ghrsc or rx_ghrsc and that they are the right device types */
> +	if ((!tx_ghrsc && !rx_ghrsc) ||
> +	    (tx_ghrsc && tx_ghrsc->type != GH_RESOURCE_TYPE_MSGQ_TX) ||
> +	    (rx_ghrsc && rx_ghrsc->type != GH_RESOURCE_TYPE_MSGQ_RX))
> +		return -EINVAL;
> +
> +	msgq->mbox.dev = parent;
> +	msgq->mbox.ops = &gh_msgq_ops;
> +	msgq->mbox.num_chans = 1;
> +	msgq->mbox.txdone_irq = true;
> +	msgq->mbox.chans = &msgq->mbox_chan;
> +
> +	ret = mbox_controller_register(&msgq->mbox);
> +	if (ret)
> +		return ret;
> +
> +	ret = mbox_bind_client(gh_msgq_chan(msgq), cl);
> +	if (ret)
> +		goto err_mbox;
> +
> +	if (tx_ghrsc) {
> +		msgq->tx_ghrsc = tx_ghrsc;
> +
> +		ret = request_irq(msgq->tx_ghrsc->irq, gh_msgq_tx_irq_handler, 0, "gh_msgq_tx",
> +				msgq);
> +		if (ret)
> +			goto err_tx_ghrsc;
> +
> +		tasklet_setup(&msgq->txdone_tasklet, gh_msgq_txdone_tasklet);
> +	}
> +
> +	if (rx_ghrsc) {
> +		msgq->rx_ghrsc = rx_ghrsc;
> +
> +		ret = request_threaded_irq(msgq->rx_ghrsc->irq, NULL, gh_msgq_rx_irq_handler,
> +						IRQF_ONESHOT, "gh_msgq_rx", msgq);
> +		if (ret)
> +			goto err_tx_irq;
> +	}
> +
> +	return 0;
> +err_tx_irq:
> +	if (msgq->tx_ghrsc)
> +		free_irq(msgq->tx_ghrsc->irq, msgq);
> +
> +	msgq->rx_ghrsc = NULL;
> +err_tx_ghrsc:
> +	msgq->tx_ghrsc = NULL;
> +err_mbox:
> +	mbox_controller_unregister(&msgq->mbox);
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(gh_msgq_init);
> +
> +void gh_msgq_remove(struct gh_msgq *msgq)
> +{
> +	if (msgq->rx_ghrsc)
> +		free_irq(msgq->rx_ghrsc->irq, msgq);
> +
> +	if (msgq->tx_ghrsc) {
> +		tasklet_kill(&msgq->txdone_tasklet);
> +		free_irq(msgq->tx_ghrsc->irq, msgq);
> +	}
> +
> +	mbox_controller_unregister(&msgq->mbox);
> +
> +	msgq->rx_ghrsc = NULL;
> +	msgq->tx_ghrsc = NULL;
> +}
> +EXPORT_SYMBOL_GPL(gh_msgq_remove);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_DESCRIPTION("Gunyah Message Queue Driver");
> diff --git a/include/linux/gunyah.h b/include/linux/gunyah.h
> index 01a6f202d037..982e27d10d57 100644
> --- a/include/linux/gunyah.h
> +++ b/include/linux/gunyah.h
> @@ -8,11 +8,68 @@
>   
>   #include <linux/bitfield.h>
>   #include <linux/errno.h>
> +#include <linux/interrupt.h>
>   #include <linux/limits.h>
> +#include <linux/mailbox_controller.h>
> +#include <linux/mailbox_client.h>
>   #include <linux/types.h>
>   
> +/* Matches resource manager's resource types for VM_GET_HYP_RESOURCES RPC */
> +enum gh_resource_type {
> +	GH_RESOURCE_TYPE_BELL_TX	= 0,
> +	GH_RESOURCE_TYPE_BELL_RX	= 1,
> +	GH_RESOURCE_TYPE_MSGQ_TX	= 2,
> +	GH_RESOURCE_TYPE_MSGQ_RX	= 3,
> +	GH_RESOURCE_TYPE_VCPU		= 4,
> +};
> +
> +struct gh_resource {
> +	enum gh_resource_type type;
> +	u64 capid;
> +	unsigned int irq;
> +};
> +
> +/**
> + * Gunyah Message Queues
> + */
> +
> +#define GH_MSGQ_MAX_MSG_SIZE		240
> +
> +struct gh_msgq_tx_data {
> +	size_t length;
> +	bool push;
> +	char data[];
> +};
> +
> +struct gh_msgq_rx_data {
> +	size_t length;
> +	char data[GH_MSGQ_MAX_MSG_SIZE];
> +};
> +
> +struct gh_msgq {
> +	struct gh_resource *tx_ghrsc;
> +	struct gh_resource *rx_ghrsc;
> +
> +	/* msgq private */
> +	int last_ret; /* Linux error, not GH_STATUS_* */
> +	struct mbox_chan mbox_chan;
> +	struct mbox_controller mbox;
> +	struct tasklet_struct txdone_tasklet;
> +};
> +
> +
> +int gh_msgq_init(struct device *parent, struct gh_msgq *msgq, struct mbox_client *cl,
> +		     struct gh_resource *tx_ghrsc, struct gh_resource *rx_ghrsc);
> +void gh_msgq_remove(struct gh_msgq *msgq);
> +
> +static inline struct mbox_chan *gh_msgq_chan(struct gh_msgq *msgq)
> +{
> +	return &msgq->mbox.chans[0];
> +}
> +
>   /******************************************************************************/
>   /* Common arch-independent definitions for Gunyah hypercalls                  */
> +
>   #define GH_CAPID_INVAL	U64_MAX
>   #define GH_VMID_ROOT_VM	0xff
>