linux-kernel - Re: [PATCH 4/4] firmware: arm_scmi: Introduce delegated xfers support

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Date:   Wed, 26 May 2021 15:53:17 +0100
From:   Cristian Marussi <cristian.marussi@....com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        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 4/4] firmware: arm_scmi: Introduce delegated xfers support

On Mon, May 24, 2021 at 07:20:45PM -0700, Florian Fainelli wrote:
> 
> 
> On 5/24/2021 4:15 PM, Cristian Marussi wrote:
> > Introduce optional support for delegated xfers allocation.
> > 
> > An SCMI transport can optionally declare to support delegated xfers and
> > then use a few helper functions exposed by the core SCMI transport layer to
> > query the core for existing in-flight transfers matching a provided message
> > header or alternatively and transparently obtain a brand new xfer to handle
> > a freshly received notification message.
> > In both cases the obtained xfer is uniquely mapped into a specific xfer
> > through the means of the message header acting as key.
> > 
> > In this way such a transport can properly store its own transport specific
> > payload into the xfer uniquely associated to the message header before
> > even calling into the core scmi_rx_callback() in the usual way, so that
> > the transport specific message envelope structures can be freed early
> > and there is no more need to keep track of their status till the core
> > fully processes the xfer to completion or times out.
> > 
> > The scmi_rx_callbak() 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>
> 
> It would be better to see this in the context of its planned user, but
> that looked reasonable enough.

I agree, definitely better to see this in the context of usage.

Such virtio-scmi rework is still in progress indeed, but working in my
local testing so far.

The reworked V4 virtio-scmi series is still to be refined and posted,
and this transitional code lives now at:

https://gitlab.arm.com/linux-arm/linux-cm/-/tree/scmi_virtio_trans_V4_rework

and in particular this is the patch that changes virtio-scmi transport to
use the new delegated xfers. (hopefully simplfying it)

https://gitlab.arm.com/linux-arm/linux-cm/-/commit/0b524f89ea6cfcf6204a5eaa8cf9030118805b2f

...but, as said, it is highly work in progress so you may just want to
wait for final V4 virtio-scmi rework posted and do not bother this noise
of mine :D

In any case thanks a lot for the feedback so far.

Cristian

> -- 
> Florian