Re: [PATCH v10 07/26] mailbox: Add Gunyah message queue mailbox

[Alex Elder]

On 2/14/23 3:23 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@xxxxxxxxxxx>
> ---
>   Documentation/virt/gunyah/message-queue.rst |   8 +
>   drivers/mailbox/Makefile                    |   2 +
>   drivers/mailbox/gunyah-msgq.c               | 214 ++++++++++++++++++++
>   include/linux/gunyah.h                      |  56 +++++
>   4 files changed, 280 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 0667b3eb1ff9..082085e981e0 100644
> --- a/Documentation/virt/gunyah/message-queue.rst
> +++ b/Documentation/virt/gunyah/message-queue.rst
> @@ -59,3 +59,11 @@ 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..03ffaa30ce9b
> --- /dev/null
> +++ b/drivers/mailbox/gunyah-msgq.c

You use a dash in this source file name, but an underscore
everywhere else.  Unless there's a good reason to do this,
please be consistent (use "gunyah_msgq.c").

> @@ -0,0 +1,214 @@
> +// 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 err;
> +	bool ready = true;
> +
> +	while (ready) {
> +		err = gh_hypercall_msgq_recv(msgq->rx_ghrsc->capid,
> +				(uintptr_t)&rx_data.data, sizeof(rx_data.data),
> +				&rx_data.length, &ready);
> +		if (err != GH_ERROR_OK) {
> +			if (err != GH_ERROR_MSGQUEUE_EMPTY)

Srini mentioned something about this too.  In many
(all?) cases, there is a device pointer available,
so you should use dev_*() functions rather than pr_*().

In this particular case, I'm not sure why/when the
mbox.dev pointer would be null.  Also, dev_*() handles
the case of a null device pointer, and it reports the
device name (just as you do here).

> +				pr_warn("Failed to receive data from msgq for %s: %d\n",
> +					msgq->mbox.dev ? dev_name(msgq->mbox.dev) : "", err);
> +			break;
> +		}
> +		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;

Above you named the variable "err".  It helps readability
if you use a very consistent naming convention for variables
of a certain type when they are used a lot.

> +	bool ready;
> +
> +	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,
> +					(uintptr_t)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_remap_error(gh_error);
> +
> +	/**
> +	 * This message was successfully sent, but message queue isn't ready to
> +	 * receive more messages because it's now full. Mailbox framework

Maybe:  s/receive/accept/

> +	 * 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 && !ready)
> +		return 0;
> +
> +	/**
> +	 * 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: optional, 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 should be not NULL. Most message queue use cases come with

s/should be/must be/

> + * 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 should register an .rx_callback() and the message queue driver will

s/should register/must register/

A general comment on this code is that you sort of half define
a Gunyah message queue API.  You define an initialization
function and an exit function, but you also expose the fact
that you use the mailbox framework in implementation.  This
despite avoiding defining it as an mbox in the DTS file.

It might be hard to avoid that I guess.  But to me it would be
nice if there were a more distinct Gunyah message queue API,
which would provide a send_message() function, for example.
And in that case, perhaps you would pass in the tx_done and/or
rx_data callbacks to this function (since they're required).

All that said, this is (currently?) only used by the resource
manager, so making a beautiful API might not be that important.
Do you envision this being used to communicate with other VMs
in the future?

> + * push all available messages upon receiving the RX ready interrupt. The messages should be

Maybe: s/push/deliver/

> + * 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 gunyah_resource *tx_ghrsc, struct gunyah_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 != GUNYAH_RESOURCE_TYPE_MSGQ_TX) ||
> +	    (rx_ghrsc && rx_ghrsc->type != GUNYAH_RESOURCE_TYPE_MSGQ_RX))
> +		return -EINVAL;
> +
> +	if (gh_api_version() != GUNYAH_API_V1) {
> +		pr_err("Unrecognized gunyah version: %u. Currently supported: %d\n",
> +			gh_api_version(), GUNYAH_API_V1);
> +		return -EOPNOTSUPP;
> +	}
> +
> +	if (!gh_api_has_feature(GH_API_FEATURE_MSGQUEUE))
> +		return -EOPNOTSUPP;

Can Gunyah even function if it doesn't have the MSGQUEUE feature?
Will there ever be a Gunyah implementation that does not support
it?  Perhaps this test could be done in gunyah_init() instead.

For that matter, you could verify the result of gh_api_version()
at that time also.

> +
> +	msgq->tx_ghrsc = tx_ghrsc;
> +	msgq->rx_ghrsc = rx_ghrsc;
> +
> +	msgq->mbox.dev = parent;
> +	msgq->mbox.ops = &gh_msgq_ops;
> +	msgq->mbox.num_chans = 1;
> +	msgq->mbox.txdone_irq = true;
> +	msgq->mbox.chans = kcalloc(msgq->mbox.num_chans, sizeof(*msgq->mbox.chans), GFP_KERNEL);

From what I can tell, you will always use exactly one mailbox channel.
So you could just do kzalloc(sizeof()...).

> +	if (!msgq->mbox.chans)
> +		return -ENOMEM;
> +
> +	if (msgq->tx_ghrsc) {

	if (tx_ghrsc) {

The irq field is assumed to be valid.  Are there any
sanity checks you could perform?  Again this is only
used for the resource manager right now, so maybe
it's OK.

> +		ret = request_irq(msgq->tx_ghrsc->irq, gh_msgq_tx_irq_handler, 0, "gh_msgq_tx",

		ret = request_irq(tx_ghrsc->irq, ...


> +				msgq);
> +		if (ret)
> +			goto err_chans;
> +	}
> +
> +	if (msgq->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;
> +	}
> +
> +	tasklet_setup(&msgq->txdone_tasklet, gh_msgq_txdone_tasklet);
> +
> +	ret = mbox_controller_register(&msgq->mbox);
> +	if (ret)
> +		goto err_rx_irq;
> +
> +	ret = mbox_bind_client(gh_msgq_chan(msgq), cl);


> +	if (ret)
> +		goto err_mbox;
> +
> +	return 0;
> +err_mbox:
> +	mbox_controller_unregister(&msgq->mbox);
> +err_rx_irq:
> +	if (msgq->rx_ghrsc)
> +		free_irq(msgq->rx_ghrsc->irq, msgq);
> +err_tx_irq:
> +	if (msgq->tx_ghrsc)
> +		free_irq(msgq->tx_ghrsc->irq, msgq);
> +err_chans:
> +	kfree(msgq->mbox.chans);
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(gh_msgq_init);
> +
> +void gh_msgq_remove(struct gh_msgq *msgq)
> +{

Is there any need to un-bind the client?

> +	mbox_controller_unregister(&msgq->mbox);
> +
> +	if (msgq->rx_ghrsc)
> +		free_irq(msgq->rx_ghrsc->irq, msgq);
> +
> +	if (msgq->tx_ghrsc)
> +		free_irq(msgq->tx_ghrsc->irq, msgq);
> +
> +	kfree(msgq->mbox.chans);
> +}
> +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 cb6df4eec5c2..2e13669c6363 100644
> --- a/include/linux/gunyah.h
> +++ b/include/linux/gunyah.h
> @@ -8,11 +8,67 @@
>   
>   #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>
>   
> +/* Follows resource manager's resource types for VM_GET_HYP_RESOURCES */
> +enum gunyah_resource_type {
> +	GUNYAH_RESOURCE_TYPE_BELL_TX	= 0,
> +	GUNYAH_RESOURCE_TYPE_BELL_RX	= 1,
> +	GUNYAH_RESOURCE_TYPE_MSGQ_TX	= 2,
> +	GUNYAH_RESOURCE_TYPE_MSGQ_RX	= 3,
> +	GUNYAH_RESOURCE_TYPE_VCPU	= 4,

The maximum value here must fit in 8 bits.  I guess
there's no risk right now of using that up, but you
use negative values in some cases elsewhere.

> +};
> +
> +struct gunyah_resource {
> +	enum gunyah_resource_type type;
> +	u64 capid;
> +	int irq;

request_irq() defines the IRQ value to be an unsigned int.

> +};
> +
> +/**
> + * 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 gunyah_resource *tx_ghrsc;
> +	struct gunyah_resource *rx_ghrsc;
> +
> +	/* msgq private */
> +	int last_ret; /* Linux error, not GH_STATUS_* */
> +	struct mbox_controller mbox;
> +	struct tasklet_struct txdone_tasklet;

Can the msgq_client be embedded here too?  (I don't really
know whether msgq and msgq_client are one-to one.)

> +};
> +
> +
> +int gh_msgq_init(struct device *parent, struct gh_msgq *msgq, struct mbox_client *cl,
> +		     struct gunyah_resource *tx_ghrsc, struct gunyah_resource *rx_ghrsc);
> +void gh_msgq_remove(struct gh_msgq *msgq);

I suggested:

int gh_msgq_send(struct gh_msgq, struct gh_msgq_tx_data *data);

					-Alex

> +
> +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
>