linux-kernel - Re: [PATCH V8 2/2] mailbox: introduce ARM SMC based mailbox

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Date:   Mon, 23 Sep 2019 19:48:27 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Peng Fan <peng.fan@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "jassisinghbrar@...il.com" <jassisinghbrar@...il.com>,
        "sudeep.holla@....com" <sudeep.holla@....com>,
        "andre.przywara@....com" <andre.przywara@....com>
Cc:     "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>
Subject: Re: [PATCH V8 2/2] mailbox: introduce ARM SMC based mailbox

Hi Peng,

On 9/23/2019 6:14 PM, 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.
> 
> Modified from Andre Przywara's v2 patch
> https://lore.kernel.org/patchwork/patch/812999/
> 
> Cc: Andre Przywara <andre.przywara@....com>
> Signed-off-by: Peng Fan <peng.fan@....com>
> ---

[snip]

> +typedef unsigned long (smc_mbox_fn)(unsigned int, unsigned long,
> +				    unsigned long, unsigned long,
> +				    unsigned long, unsigned long,
> +				    unsigned long);
> +static smc_mbox_fn *invoke_smc_mbox_fn;

Sorry for spotting this so late, the only thing that concerns me here
with this singleton is if we happen to have both an arm,smc-mbox and
arm,hvc-mbox configured in the system, this would not work. I do not
believe this could be a functional use case, but we should probably
guard against that or better yet, move that into the arm_smc_chan_data
private structure?
-- 
Florian