[v8,09/28] 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 +
 MAINTAINERS                                 |   1 +
 drivers/mailbox/Kconfig                     |  10 +
 drivers/mailbox/Makefile                    |   2 +
 drivers/mailbox/gunyah-msgq.c               | 229 ++++++++++++++++++++
 include/linux/gunyah.h                      |  61 +++++-
 6 files changed, 309 insertions(+), 2 deletions(-)
 create mode 100644 drivers/mailbox/gunyah-msgq.c

* Elliot Berman <quic_eberman@quicinc.com> [2022-12-19 14:58:30]:

> +static inline bool gh_msgq_has_tx(struct gh_msgq *msgq)
> +{

Consider possibility that msgq->tx_ghrc can be NULL?

> +	return msgq->tx_ghrsc->type == GUNYAH_RESOURCE_TYPE_MSGQ_TX;
> +}
> +
> +static inline bool gh_msgq_has_rx(struct gh_msgq *msgq)
> +{

Consider possibility that msgq->rx_ghrc can be NULL?

> +	return msgq->rx_ghrsc->type == GUNYAH_RESOURCE_TYPE_MSGQ_RX;
> +}
> +
> +static irqreturn_t gh_msgq_rx_irq_handler(int irq, void *data)
> +{
> +	struct gh_msgq *msgq = data;
> +	struct gh_msgq_rx_data rx_data;
> +	unsigned long gh_err;
> +	ssize_t ret;
> +	bool ready = false;
> +
> +	do {
> +		gh_err = gh_hypercall_msgq_recv(msgq->rx_ghrsc->capid,
> +				(uintptr_t)&rx_data.data, sizeof(rx_data.data),
> +				&rx_data.length, &ready);
> +		if (gh_err == GH_ERROR_OK) {
> +			mbox_chan_received_data(gh_msgq_chan(msgq), &rx_data);
> +		} else if (GH_ERROR_MSGQUEUE_EMPTY) {

gh_err == GH_ERROR_MSGQUEUE_EMPTY 

> +			break;
> +		} else {
> +			pr_warn("Failed to receive data from msgq for %s: %ld\n",
> +				msgq->mbox.dev ? dev_name(msgq->mbox.dev) : "", ret);
> +			break;
> +		}
> +	} while (ready);
> +
> +	return IRQ_HANDLED;
> +}

On 1/1/2023 10:13 PM, Srivatsa Vaddagiri wrote:
> * Elliot Berman <quic_eberman@quicinc.com> [2022-12-19 14:58:30]:
> 
>> +static inline bool gh_msgq_has_tx(struct gh_msgq *msgq)
>> +{
> 
> Consider possibility that msgq->tx_ghrc can be NULL?
> 
>> +	return msgq->tx_ghrsc->type == GUNYAH_RESOURCE_TYPE_MSGQ_TX;
>> +}
>> +
>> +static inline bool gh_msgq_has_rx(struct gh_msgq *msgq)
>> +{
> 
> Consider possibility that msgq->rx_ghrc can be NULL?
> 
>> +	return msgq->rx_ghrsc->type == GUNYAH_RESOURCE_TYPE_MSGQ_RX;
>> +}
>> +
>> +static irqreturn_t gh_msgq_rx_irq_handler(int irq, void *data)
>> +{
>> +	struct gh_msgq *msgq = data;
>> +	struct gh_msgq_rx_data rx_data;
>> +	unsigned long gh_err;
>> +	ssize_t ret;
>> +	bool ready = false;
>> +
>> +	do {
>> +		gh_err = gh_hypercall_msgq_recv(msgq->rx_ghrsc->capid,
>> +				(uintptr_t)&rx_data.data, sizeof(rx_data.data),
>> +				&rx_data.length, &ready);
>> +		if (gh_err == GH_ERROR_OK) {
>> +			mbox_chan_received_data(gh_msgq_chan(msgq), &rx_data);
>> +		} else if (GH_ERROR_MSGQUEUE_EMPTY) {
> 
> gh_err == GH_ERROR_MSGQUEUE_EMPTY
> 

Applied the 3 comments, thanks!

On 1/9/2023 1:34 PM, Alex Elder wrote:
> On 12/19/22 4:58 PM, Elliot Berman wrote:
>> Gunyah message queues are a unidirectional inter-VM pipe for messages up
> 
> s/Gunyah message queues are/A Gunyah message queue is/
> 
>> 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 +
>>   MAINTAINERS                                 |   1 +
>>   drivers/mailbox/Kconfig                     |  10 +
>>   drivers/mailbox/Makefile                   |   2 +
>>   drivers/mailbox/gunyah-msgq.c               | 229 ++++++++++++++++++++
>>   include/linux/gunyah.h                      |  61 +++++-
>>   6 files changed, 309 insertions(+), 2 deletions(-)
>>   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 be4ab289236a..9245dbe6dd8a 100644
>> --- a/Documentation/virt/gunyah/message-queue.rst
>> +++ b/Documentation/virt/gunyah/message-queue.rst
>> @@ -54,3 +54,11 @@ 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/MAINTAINERS b/MAINTAINERS
>> index 36698df6b0e5..667480bfd387 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -8942,6 +8942,7 @@ S:    Supported
>>   F:    Documentation/devicetree/bindings/firmware/gunyah-hypervisor.yaml
>>   F:    Documentation/virt/gunyah/
>>   F:    arch/arm64/gunyah/
>> +F:    drivers/mailbox/gunyah-msgq.c
>>   F:    drivers/virt/gunyah/
>>   F:    include/linux/gunyah.h
>> diff --git a/drivers/mailbox/Kconfig b/drivers/mailbox/Kconfig
>> index 05d6fae800e3..baf9451c5f04 100644
>> --- a/drivers/mailbox/Kconfig
>> +++ b/drivers/mailbox/Kconfig
>> @@ -41,6 +41,16 @@ config IMX_MBOX
>>       help
>>         Mailbox implementation for i.MX Messaging Unit (MU).
>> +config GUNYAH_MESSAGE_QUEUES
> 
> Is Gunyah useful without message queues? Are Gunyah message
> queues useful without the rest of Gunyah?  Are there other
> possible message queue implementations?  My point is that
> maybe this isn't a necessary kernel config option.
> 

I can drop this.

>> +    tristate "Gunyah Message Queue Mailbox"
>> +    depends on GUNYAH
>> +    help
>> +      Mailbox implementation for Gunyah Message Queues. Gunyah 
>> message queues
>> +      are an IPC mechanism to pass short messages between virtual 
>> machines
>> +      running under the Gunyah hypervisor.
>> +
>> +      Say Y here if you run Linux as a Gunyah virtual machine.
>> +
>>   config PLATFORM_MHU
>>       tristate "Platform MHU Mailbox"
>>       depends on OF
>> 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-$(CONFIG_GUNYAH)        += gunyah-msgq.o
> 
> Assuming you keep the Kconfig option, should this be
> referring to CONFIG_GUNYAH_MESSAGE_QUEUES?
> 
>> +
>>   obj-$(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..d5a324e85428
>> --- /dev/null
>> +++ b/drivers/mailbox/gunyah-msgq.c
>> @@ -0,0 +1,229 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * Copyright (c) 2022 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 inline bool gh_msgq_has_tx(struct gh_msgq *msgq)
>> +{
>> +    return msgq->tx_ghrsc->type == GUNYAH_RESOURCE_TYPE_MSGQ_TX;
> 
> I think this was pointed out elsewhere; I think msgq->tx_ghrsc
> can be null.  Same for msgq->rx_ghrsc below.
> 
>> +}
>> +
>> +static inline bool gh_msgq_has_rx(struct gh_msgq *msgq)
>> +{
>> +    return msgq->rx_ghrsc->type == GUNYAH_RESOURCE_TYPE_MSGQ_RX;
> 
> Is there any chance that a message queue would be created whose
> type was anything other than MSGQ_RX?  It's possible that there
> is some generic resource code that needs this type field, but
> in this case I don't see why it's important.
> 
> And...  If that's the case, I think it's perhaps clearer to
> just replace calls to gs_msgq_has_rx(msgq) with:
> 
>      if (msgq->rx_ghrsc)
>          /* there is an RX message queue */
> 

Yep, that's what I've done for v9.

>> +}
>> +
>> +static irqreturn_t gh_msgq_rx_irq_handler(int irq, void *data)
>> +{
>> +    struct gh_msgq *msgq = data;
>> +    struct gh_msgq_rx_data rx_data;
>> +    unsigned long gh_err;
>> +    ssize_t ret;
>> +    bool ready = false;
>> +
>> +    do {
> 
> Maybe:    bool ready = true;
> 
>      while (ready) {
>> +        gh_err = gh_hypercall_msgq_recv(msgq->rx_ghrsc->capid,
>> +                (uintptr_t)&rx_data.data, sizeof(rx_data.data),
>> +                &rx_data.length, &ready);
>> +        if (gh_err == GH_ERROR_OK) {
>> +            mbox_chan_received_data(gh_msgq_chan(msgq), &rx_data);
> 
> Maybe            continue;
>          }
> 
>          if (gh_err != GH_ERROR_MSGQUEUE_EMPTY)
>              pr_warn(...);
> 
>          break;
> 
>> +        } else if (GH_ERROR_MSGQUEUE_EMPTY) {
>> +            break;
>> +        } else {
>> +            pr_warn("Failed to receive data from msgq for %s: %ld\n",
> 
> s/%ld/%zd/
> 
>> +                msgq->mbox.dev ? dev_name(msgq->mbox.dev) : "", ret);
>> +            break;
>> +        }
>> +    } while (ready);
>> +
>> +    return IRQ_HANDLED;
>> +}
>> +
>> +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;
>> +}
>> +
>> +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_status);
>> +}
>> +
>> +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;
>> +    unsigned long ret;
>> +    bool ready;
>> +
>> +    if (msgq_data->push)
>> +        tx_flags |= GH_HYPERCALL_MSGQ_TX_FLAGS_PUSH;
>> +
> 
> I probably missed something, but where is gh_hypercall_msgq_send()
> defined?  I'm interested in what the ready flag is used for.
> (Can the return value encode that?)
> 

It's in arch/arm64/gunyah/gunyah_hypercall.c. The return values of 
encode whether more data can be received (ready flag).

>> +    ret = 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.
>> +     */
> 
> Is it just unlikely, or is it impossible?
> 

This would require multiple mailbox controllers interacting with the 
same message queue.

The only way I can think this is possible is if the Gunyah drivers are 
unloaded when the message queue is full; drivers are then re-loaded 
before the receiver processes the messages. The initial internal state 
of the message queue controller assumes that there is space in the 
message queue. We would get a Tx vIRQ once space becomes available and 
the message would then be attempted to sent again. Since there's a safe 
flow to recover from a inconsistent internal state and it's very 
unlikely to start in that state, I don't think we need to add calls to 
check if the message queue is full during initialization.

>> +    if (unlikely(ret == 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_status = gh_remap_error(ret);
>> +
>> +    /**
>> +     * This message was successfully sent, but message queue isn't 
>> ready to
>> +     * receive more messages because it's now full.Mailbox framework
>> +     * requires that we only report that message was transmitted only 
>> when
> 
> s/only //    (for one of them)
> 
>> +     * 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 (ret == GH_ERROR_OK && !ready)
>> +        return 0;
>> +
>> +    /**
>> +     * We can send more messages. Mailbox frameworkrequires 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;
>> +}
>> +
>> +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
>> + * a pair of message queues to facilitiate bidirectional 
>> communication. When tx_ghrsc is set,
> 
> s/facilitiate/facilitate/
> 
>> + * 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
>> + * push 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 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))
> 
> The internal parenthesis pairs above aren't really required.
> 
> 

I think it's cleaner/easier to read this way.

>> +        return -EINVAL;
>> +
>> +    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.chans = kcalloc(msgq->mbox.num_chans, 
>> sizeof(*msgq->mbox.chans), GFP_KERNEL);
>> +    if (!msgq->mbox.chans)
>> +        return -ENOMEM;
>> +    msgq->mbox.txdone_irq = true;
>> +
>> +    if (gh_msgq_has_tx(msgq)) {
> 
> Maybe    if (tx_ghrsc) {
> 
>> +        ret = request_irq(msgq->tx_ghrsc->irq, 
>> gh_msgq_tx_irq_handler, 0, "gh_msgq_tx",
>> +                msgq);
>> +        if (ret)
>> +            gotoerr_chans;
>> +    }
>> +
>> +    if (gh_msgq_has_rx(msgq)) {
> 
> Maybe    if (rx_ghrsc) {
> 
>> +        ret = request_threaded_irq(msgq->rx_ghrsc->irq, NULL, 
>> gh_msgq_rx_irq_handler,
>> +                        IRQF_ONESHOT, "gh_msgq_rx", msgq);
>> +        if (ret)
>> +            gotoerr_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 (gh_msgq_has_rx(msgq))
> 
>      if (rx_ghrsc)
> 
>> +        free_irq(msgq->rx_ghrsc->irq, msgq);
>> +err_tx_irq:
>> +    if (gh_msgq_has_tx(msgq))
> 
>      if (tx_ghrsc)
> 

Applied for the suggestions above.

>> +        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)
>> +{
>> +    mbox_controller_unregister(&msgq->mbox);
>> +
>> +    if (gh_msgq_has_rx(msgq))
>> +        free_irq(msgq->rx_ghrsc->irq, msgq);
>> +
>> +    if (gh_msgq_has_tx(msgq))
>> +        free_irq(msgq->tx_ghrsc->irq, msgq);
>> +
>> +    kfree(msgq->mbox.chans);
>> +}
>> +EXPORT_SYMBOL_GPL(gh_msgq_remove);
>> +
>> +
>> +static int __init gh_msgq_init_module(void)
>> +{
>> +    if (gh_api_version() != GUNYAH_API_V1) {
>> +        pr_warn("Unrecognized gunyahversion: %u. Currently 
>> supported: %d\n",
>> +            gh_api_version(), GUNYAH_API_V1);
>> +        return -ENODEV;
>> +    }
>> +
>> +    return 0;
>> +}
>> +module_init(gh_msgq_init_module);
>> +
>> +MODULE_LICENSE("GPL");
>> +MODULE_DESCRIPTION("Gunyah Message Queue Driver");
>> diff --git a/include/linux/gunyah.h b/include/linux/gunyah.h
>> index c863cac4a3cf..e317d7ac938f 100644
>> --- a/include/linux/gunyah.h
>> +++ b/include/linux/gunyah.h
>> @@ -7,10 +7,67 @@
>>   #define _GUNYAH_H
>>   #include <linux/bitfield.h>
>> -#include <linux/types.h>
>>   #include <linux/errno.h>
>> +#include <linux/interrupt.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,
>> +};
>> +
>> +struct gunyah_resource {
>> +    enum gunyah_resource_type type;
>> +    u64 capid;
>> +    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 gunyah_resource *tx_ghrsc;
>> +    struct gunyah_resource *rx_ghrsc;
>> +
>> +    /* msgq private */
>> +    int last_status;
> 
> Maybe note that last_status is an errno (and not GH_ERROR_*)
> 

Done, renamed to "last_ret".

>                      -Alex
> 
>> +    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 gunyah_resource *tx_ghrsc, struct gunyah_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 macros and definitions for Gunyah 
>> hypercalls */
>> -/* Common Gunyah macros */
>>   #define GH_CAPID_INVAL    U64_MAX
>>   #define GH_VMID_ROOT_VM    0xff
>

On 1/10/23 12:16 PM, Elliot Berman wrote:
>>> +    ret = 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.
>>> +     */
>>
>> Is it just unlikely, or is it impossible?
>>
> 
> This would require multiple mailbox controllers interacting with the 
> same message queue.
> 
> The only way I can think this is possible is if the Gunyah drivers are 
> unloaded when the message queue is full; drivers are then re-loaded 
> before the receiver processes the messages. The initial internal state 
> of the message queue controller assumes that there is space in the 
> message queue. We would get a Tx vIRQ once space becomes available and 
> the message would then be attempted to sent again. Since there's a safe 
> flow to recover from a inconsistent internal state and it's very 
> unlikely to start in that state, I don't think we need to add calls to 
> check if the message queue is full during initialization.

First, your explanation is appreciated but more than what I
was looking for...  I just mentioned it because if it were
impossible, then there's no point in having this code handle
something that literally can't happen.

But as far as your explanation, I *hope* if the Gunyah drivers
are unloaded, everything gets fully cleaned up before that
completes.  There should be no in-flight activity, or
any "previous generation" messages that could be processed.

In any case, I think my question is answered.  Thanks.

					-Alex