linux-kernel - Re: [PATCH v4 11/12] [RFC] firmware: arm_scmi: Add sync_cmds_atomic

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Date:   Wed, 25 Aug 2021 18:38:19 +0200
From:   Florian Fainelli <f.fainelli@...il.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, etienne.carriere@...aro.org,
        vincent.guittot@...aro.org, souvik.chakravarty@....com
Subject: Re: [PATCH v4 11/12] [RFC] firmware: arm_scmi: Add
 sync_cmds_atomic_replies transport flag



On 8/24/2021 3:59 PM, Cristian Marussi wrote:
> A flag is added to let the transport signal the core that its handling of
> synchronous command messages implies that, after .send_message has returned
> successfully, the requested command can be assumed to be fully and
> completely executed on SCMI platform side so that any possible response
> value is already immediately available to be retrieved by a .fetch_reponse:
> in other words the polling phase can be skipped in such a case and the
> response values accessed straight away.
> 
> Note that all of the above applies only when polling mode of operation was
> selected by the core: if instead a completion IRQ was found to be available
> the normal response processing path based on completions will still be
> followed.

This might actually have to be settable on a per-message basis ideally 
since we may be transporting short lived SCMI messages for which the 
completion can be done at SMC time, and long lived SCMI messages (e.g.: 
involving a voltage change) for which we would prefer a completion 
interrupt. Jim, what do you think?
-- 
Florian