linux-kernel - Re: [PATCH v5 08/15] firmware: arm_scmi: Introduce optional support for delegated xfers

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Message-ID: <20210706141841.GG17807@e120937-lin>
Date:   Tue, 6 Jul 2021 15:18:41 +0100
From:   Cristian Marussi <cristian.marussi@....com>
To:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        virtualization@...ts.linux-foundation.org,
        virtio-dev@...ts.oasis-open.org
Cc:     sudeep.holla@....com, james.quinlan@...adcom.com,
        Jonathan.Cameron@...wei.com, f.fainelli@...il.com,
        etienne.carriere@...aro.org, vincent.guittot@...aro.org,
        souvik.chakravarty@....com, igor.skalkin@...nsynergy.com,
        peter.hilber@...nsynergy.com, alex.bennee@...aro.org,
        jean-philippe@...aro.org, mikhail.golubev@...nsynergy.com,
        anton.yakovlev@...nsynergy.com, Vasyl.Vavrychuk@...nsynergy.com,
        Andriy.Tryshnivskyy@...nsynergy.com
Subject: Re: [PATCH v5 08/15] firmware: arm_scmi: Introduce optional support
 for delegated xfers

On Mon, Jul 05, 2021 at 03:49:07PM +0100, Cristian Marussi wrote:
> Some SCMI transports allow for more parallelism while handling SCMI
> messages and as a result may have more complex inner workings than shared
> memory based transports and they could need to maintain additional
> transport-specific state information and data about the ongoing transfers.
> Using the current SCMI core transport layer interface, additional effort
> would be needed to keep such states and data in sync with the SCMI core.
> 
> Allow an SCMI transport to optionally declare to be using delegated xfers
> so that it can use a few SCMI core helper functions to query the core early
> on in the RX path for any valid existing in-flight transfers matching a
> specific message header or, alternatively, to transparently obtain a brand
> new dedicated xfer to handle a notification message.
> 
> In both cases the obtained xfer can be uniquely mapped to a specific xfer,
> assured to be valid, through the means of the message header sequence
> number acting as key.
> 
> In this way such a transport can save its own transport specific envelope
> into a private reference associated with the xfer before calling into the
> core scmi_rx_callback() in the usual way.
> 
> The scmi_rx_callback() does not need to be modified to carry additional
> transport-specific ancillary data related to such message envelopes since
> an unique natural association is established between the xfer and the
> related message header.
> 
> Existing transports that do not need anything of the above will continue
> to work as before without any change.
> 
> Signed-off-by: Cristian Marussi <cristian.marussi@....com>
> ---

Hi,

as an afterthough (sigh...) on this patch of mine, I think that now, after
all the support introduced earlier within this same series into the SCMI
core (monotonic tokens and concurrency/out-of-order handling of responses),
the additional complexity of this patch could NOT be needed anymore and I
am actually experimenting dropping this patch as a whole and further
simplifying the virtio transport rx logic, with the only caveat of
having to modify scmi_rx_callback() prototype to allow for a new
priv parameter to be optionally provided by the transport, thing that I
avoided till now but it does not seem worth anymore.

I'll post a new V6 on 5.14-rc1 with this patch reworked once fully
tested and ruled out any unexpected surprise.

Sorry for the noise.

Thanks,
Cristian