linux-kernel - Re: [PATCH v4 07/13] firmware: arm_scmi: Add notification dispatch and delivery

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Date:   Thu, 12 Mar 2020 13:51:52 +0000
From:   Lukasz Luba <lukasz.luba@....com>
To:     Cristian Marussi <cristian.marussi@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     sudeep.holla@....com, james.quinlan@...adcom.com,
        Jonathan.Cameron@...wei.com
Subject: Re: [PATCH v4 07/13] firmware: arm_scmi: Add notification dispatch
 and delivery

Hi Cristian,

just one comment below...

On 3/4/20 4:25 PM, Cristian Marussi wrote:
> Add core SCMI Notifications dispatch and delivery support logic which is
> able, at first, to dispatch well-known received events from the RX ISR to
> the dedicated deferred worker, and then, from there, to final deliver the
> events to the registered users' callbacks.
> 
> Dispatch and delivery is just added here, still not enabled.
> 
> Signed-off-by: Cristian Marussi <cristian.marussi@....com>
> ---
> V3 --> V4
> - dispatcher now handles dequeuing of events in chunks (header+payload):
>    handling of these in_flight events let us remove one unneeded memcpy
>    on RX interrupt path (scmi_notify)
> - deferred dispatcher now access their own per-protocol handlers' table
>    reducing locking contention on the RX path
> V2 --> V3
> - exposing wq in sysfs via WQ_SYSFS
> V1 --> V2
> - splitted out of V1 patch 04
> - moved from IDR maps to real HashTables to store event_handlers
> - simplified delivery logic
> ---
>   drivers/firmware/arm_scmi/notify.c | 334 ++++++++++++++++++++++++++++-
>   drivers/firmware/arm_scmi/notify.h |   9 +
>   2 files changed, 342 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/arm_scmi/notify.c b/drivers/firmware/arm_scmi/notify.c

[snip]

> +
> +/**
> + * scmi_notify  - Queues a notification for further deferred processing
> + *
> + * This is called in interrupt context to queue a received event for
> + * deferred processing.
> + *
> + * @handle: The handle identifying the platform instance from which the
> + *	    dispatched event is generated
> + * @proto_id: Protocol ID
> + * @evt_id: Event ID (msgID)
> + * @buf: Event Message Payload (without the header)
> + * @len: Event Message Payload size
> + * @ts: RX Timestamp in nanoseconds (boottime)
> + *
> + * Return: 0 on Success
> + */
> +int scmi_notify(const struct scmi_handle *handle, u8 proto_id, u8 evt_id,
> +		const void *buf, size_t len, u64 ts)
> +{
> +	struct scmi_registered_event *r_evt;
> +	struct scmi_event_header eh;
> +	struct scmi_notify_instance *ni = handle->notify_priv;
> +
> +	/* Ensure atomic value is updated */
> +	smp_mb__before_atomic();
> +	if (unlikely(!atomic_read(&ni->enabled)))
> +		return 0;
> +
> +	r_evt = SCMI_GET_REVT(ni, proto_id, evt_id);
> +	if (unlikely(!r_evt))
> +		return -EINVAL;
> +
> +	if (unlikely(len > r_evt->evt->max_payld_sz)) {
> +		pr_err("SCMI Notifications: discard badly sized message\n");
> +		return -EINVAL;
> +	}
> +	if (unlikely(kfifo_avail(&r_evt->proto->equeue.kfifo) <
> +		     sizeof(eh) + len)) {
> +		pr_warn("SCMI Notifications: queue full dropping proto_id:%d  evt_id:%d  ts:%lld\n",
> +			proto_id, evt_id, ts);
> +		return -ENOMEM;
> +	}
> +
> +	eh.timestamp = ts;
> +	eh.evt_id = evt_id;
> +	eh.payld_sz = len;
> +	kfifo_in(&r_evt->proto->equeue.kfifo, &eh, sizeof(eh));
> +	kfifo_in(&r_evt->proto->equeue.kfifo, buf, len);
> +	queue_work(r_evt->proto->equeue.wq,
> +		   &r_evt->proto->equeue.notify_work);

Is it safe to ignore the return value from the queue_work here?

Regards,
Lukasz