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

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Message-ID: <AM0PR04MB448140416B9AFD18051A7E84885C0@AM0PR04MB4481.eurprd04.prod.outlook.com>
Date:   Thu, 5 Dec 2019 03:24:14 +0000
From:   Peng Fan <peng.fan@....com>
To:     Sudeep Holla <sudeep.holla@....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>,
        Arnd Bergmann <arnd@...db.de>
Subject: RE: [PATCH v11 2/2] mailbox: introduce ARM SMC based mailbox

> 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 ? 

Currently my usecase is SCMI.

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.

If we want to use SMC as transports, smc mailbox or smc transports(non-mailbox)
could be used. Both ok for me, smc transports just need write a new driver
under scmi folder.

I left the decision to you(scmi maintainer) and Jassi(mailbox maintainer),
Just hope the smc/hvc used as transports could be landed in upstream soon.

Thanks,
Peng.

> 
> --
> Regards,
> Sudeep
> 
> [1]
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.ke
> rnel.org%2Flkml%2F5c545c2866ba075ddb44907940a1dae1d823b8a1.15750
> 19719.git.viresh.kumar%40linaro.org&amp;data=02%7C01%7Cpeng.fan%40n
> xp.com%7C06edb0c37371419db3cd08d777e66780%7C686ea1d3bc2b4c6fa9
> 2cd99c5c301635%7C0%7C1%7C637109703766574454&amp;sdata=nInLSUu
> mwzBvl%2FcmckQkpZbJT4JAtVkzr1TSWkmz6qo%3D&amp;reserved=0