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

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Date:   Wed, 25 Aug 2021 13:17:47 -0400
From:   Jim Quinlan <james.quinlan@...adcom.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Cristian Marussi <cristian.marussi@....com>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        etienne.carriere@...aro.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Souvik Chakravarty <souvik.chakravarty@....com>
Subject: Re: [PATCH v4 11/12] [RFC] firmware: arm_scmi: Add
 sync_cmds_atomic_replies transport flag

On Wed, Aug 25, 2021 at 12:38 PM Florian Fainelli <f.fainelli@...il.com> wrote:
>
>
>
> 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?
Even if the SCMI main driver could be configured this way in an
elegant manner, I'm not sure that there is a clean way of specifying
this  attribute on a per-message basis.  Certainly we could do this
with our own protocols, but  many of our "long lived" messages are the
Perf protocol's set_level command.  At any rate, let me give it some
thought.

Regards,
Jim
> --
> Florian

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