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

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Date:   Thu, 12 Mar 2020 14:06:58 +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



On 3/12/20 1:51 PM, Lukasz Luba wrote:
> 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?

and also from the kfifo_in

> 
> Regards,
> Lukasz
> 
>