linux-kernel - Re: [PATCH v11 2/2] mailbox: introduce ARM SMC based mailbox

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Date:   Tue, 3 Dec 2019 11:46:07 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Peng Fan <peng.fan@....com>
Cc:     "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "jassisinghbrar@...il.com" <jassisinghbrar@...il.com>,
        "andre.przywara@....com" <andre.przywara@....com>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        dl-linux-imx <linux-imx@....com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v11 2/2] mailbox: introduce ARM SMC based mailbox

(+Viresh,Arnd)

On Mon, Dec 02, 2019 at 10:14:43AM +0000, Peng Fan wrote:
> From: Peng Fan <peng.fan@....com>
>
> This mailbox driver implements a mailbox which signals transmitted data
> via an ARM smc (secure monitor call) instruction. The mailbox receiver
> is implemented in firmware and can synchronously return data when it
> returns execution to the non-secure world again.
> An asynchronous receive path is not implemented.
> This allows the usage of a mailbox to trigger firmware actions on SoCs
> which either don't have a separate management processor or on which such
> a core is not available. A user of this mailbox could be the SCP
> interface.
>

I would like to know all the use-cases for this driver ? Is this only for
SCMI or will this get used with other protocols on the top. I assume the
latter and hence it is preferred to keep this as a mailbox driver.

I am not against this approach but the reason I ask is to avoid duplication.
Viresh has suggested abstraction of transport from SCMI driver to enable
other transports[1]. Couple of transports that I am aware of is this SMC/HVC
and the new(still in-concept) SPCI.

So I am looking for opinions on that approach. Please feel free to comment
here or as part of that patch.

--
Regards,
Sudeep

[1] https://lore.kernel.org/lkml/5c545c2866ba075ddb44907940a1dae1d823b8a1.1575019719.git.viresh.kumar@linaro.org