linux-kernel - Re: [PATCH v5 1/2] dt-bindings: mailbox: add binding doc for the ARM SMC/HVC mailbox

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Message-ID: <20190830093005.GA31297@bogus>
Date:   Fri, 30 Aug 2019 10:30:05 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Peng Fan <peng.fan@....com>
Cc:     Jassi Brar <jassisinghbrar@...il.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....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>,
        Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH v5 1/2] dt-bindings: mailbox: add binding doc for the ARM
 SMC/HVC mailbox

On Fri, Aug 30, 2019 at 07:37:41AM +0000, Peng Fan wrote:
> Hi Jassi,
> > > I think there could be channel for TEE, and channel for Linux.
> > > For virtualization case, there could be dedicated channel for each VM.
> > >
> > I am talking from Linux pov. Functions 0xfe and 0xff above, can't both be
> > active at the same time, right?
>
> If I get your point correctly,
> On UP, both could not be active. On SMP, tx/rx could be both active, anyway
> this depends on secure firmware and Linux firmware design.
>

Just to confirm, we can't have SMC/HVC based Rx channel as there's no
*architectural* way to achieve it. So it can be based on some interrupt
from secure side and hence will be a *different* type of channel/controller.

Sorry to make this point repeatedly, but juts to be absolutely clear:
as it stands, SMC/HVC can be used only for Tx today.

--
Regards,
Sudeep