Date:   Tue, 1 Nov 2022 10:44:59 -0700
From:   Elliot Berman <quic_eberman@...cinc.com>
To:     Pavan Kondeti <quic_pkondeti@...cinc.com>
CC:     Bjorn Andersson <quic_bjorande@...cinc.com>,
        Jassi Brar <jassisinghbrar@...il.com>,
        Murali Nalajala <quic_mnalajal@...cinc.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        Srivatsa Vaddagiri <quic_svaddagi@...cinc.com>,
        Carl van Schaik <quic_cvanscha@...cinc.com>,
        Prakruthi Deepak Heragu <quic_pheragu@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Marc Zyngier <maz@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Jonathan Corbet <corbet@....net>,
        "Will Deacon" <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "Arnd Bergmann" <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Amol Maheshwari <amahesh@....qualcomm.com>,
        Kalle Valo <kvalo@...nel.org>, <devicetree@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 09/21] mailbox: Add Gunyah message queue mailbox


On 10/27/2022 6:55 AM, Pavan Kondeti wrote:
> Hi Elliot,
> 
> On Wed, Oct 26, 2022 at 11:58:34AM -0700, 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@...cinc.com>
> 
> <snip>
> 
>> +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(unsigned long data)
>> +{
>> +	struct gh_msgq *msgq = (struct gh_msgq *)data;
>> +
>> +	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;
>> +
>> +	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.
>> +	 */
>> +	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
>> +	 * 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 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);
>> +
> 
> Nice comments.
> 
> irq_work would be a better choice.
> 
>> +	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,
>> + * 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))
>> +		return -EINVAL;
>> +
>> +	msgq->tx_ghrsc = tx_ghrsc;
>> +	msgq->rx_ghrsc = rx_ghrsc;
>> +
>> +	msgq->mbox.dev = parent;
>> +	msgq->mbox.ops = &gh_msgq_ops;
>> +	msgq->mbox.chans = kcalloc(1, sizeof(*msgq->mbox.chans), GFP_KERNEL);
> 
> Error handling missing.
> 
> minor nit pick:
> 
> If you initialize num_chans to 1 before, then you can use that as the first
> argument to kcalloc() which makes it more readable since you opted for kcalloc()
> instead of kzalloc() there.
> 
>> +	msgq->mbox.num_chans = 1;
>> +	msgq->mbox.txdone_irq = true;
>> +
>> +	if (gh_msgq_has_tx(msgq)) {
>> +		ret = request_irq(msgq->tx_ghrsc->irq, gh_msgq_tx_irq_handler, 0, "gh_msgq_tx",
>> +				msgq);
>> +		if (ret)
>> +			goto err_chans;
>> +	}
>> +
>> +	if (gh_msgq_has_rx(msgq)) {
>> +		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_init(&msgq->txdone_tasklet, gh_msgq_txdone_tasklet, (unsigned long)msgq);
> 
> If you wish to use tasklets, use tasklet_setup().
> 
>> +
>> +	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))
>> +		free_irq(msgq->rx_ghrsc->irq, msgq);
>> +err_tx_irq:
>> +	if (gh_msgq_has_tx(msgq))
>> +		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)
>> +{
>> +	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);
>> +
> 
> Is gh_msgq_remove() supposed to undo every thing done in gh_msgq_init()?
> ex: mbox controller and channel are not unregistered.
> 

Ah thanks for catching, updated this as well as rest of your comments.

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