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: <CABb+yY2t-oz6KqvCTsOJZqcMAUaR9Cbj014m7dCFXSBAMCojww@mail.gmail.com>
Date:   Fri, 30 Aug 2019 03:12:29 -0500
From:   Jassi Brar <jassisinghbrar@...il.com>
To:     Peng Fan <peng.fan@....com>
Cc:     "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "sudeep.holla@....com" <sudeep.holla@....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>
Subject: Re: [PATCH v5 1/2] dt-bindings: mailbox: add binding doc for the ARM
 SMC/HVC mailbox

On Fri, Aug 30, 2019 at 3:07 AM Peng Fan <peng.fan@....com> wrote:
>
> > Subject: Re: [PATCH v5 1/2] dt-bindings: mailbox: add binding doc for the ARM
> > SMC/HVC mailbox
> >
> > On Fri, Aug 30, 2019 at 2:37 AM Peng Fan <peng.fan@....com> wrote:
> > >
> > > Hi Jassi,
> > >
> > > > Subject: Re: [PATCH v5 1/2] dt-bindings: mailbox: add binding doc
> > > > for the ARM SMC/HVC mailbox
> > > >
> > > > On Fri, Aug 30, 2019 at 1:28 AM Peng Fan <peng.fan@....com> wrote:
> > > >
> > > > > > > +examples:
> > > > > > > +  - |
> > > > > > > +    sram@...000 {
> > > > > > > +      compatible = "mmio-sram";
> > > > > > > +      reg = <0x0 0x93f000 0x0 0x1000>;
> > > > > > > +      #address-cells = <1>;
> > > > > > > +      #size-cells = <1>;
> > > > > > > +      ranges = <0 0x0 0x93f000 0x1000>;
> > > > > > > +
> > > > > > > +      cpu_scp_lpri: scp-shmem@0 {
> > > > > > > +        compatible = "arm,scmi-shmem";
> > > > > > > +        reg = <0x0 0x200>;
> > > > > > > +      };
> > > > > > > +
> > > > > > > +      cpu_scp_hpri: scp-shmem@200 {
> > > > > > > +        compatible = "arm,scmi-shmem";
> > > > > > > +        reg = <0x200 0x200>;
> > > > > > > +      };
> > > > > > > +    };
> > > > > > > +
> > > > > > > +    firmware {
> > > > > > > +      smc_mbox: mailbox {
> > > > > > > +        #mbox-cells = <1>;
> > > > > > > +        compatible = "arm,smc-mbox";
> > > > > > > +        method = "smc";
> > > > > > > +        arm,num-chans = <0x2>;
> > > > > > > +        transports = "mem";
> > > > > > > +        /* Optional */
> > > > > > > +        arm,func-ids = <0xc20000fe>, <0xc20000ff>;
> > > > > > >
> > > > > > SMC/HVC is synchronously(block) running in "secure mode", i.e,
> > > > > > there can only be one instance running platform wide. Right?
> > > > >
> > > > > 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.
> > >
> > > Do you have any suggestions about arm,func-ids here?
> > >
> > I was thinking if this is just an instruction, why can't each channel be
> > represented as a controller, i.e, have exactly one func-id per controller node.
> > Define as many controllers as you need channels ?
>
> I am ok, this could make driver code simpler. Something as below?
>
>     smc_tx_mbox: tx_mbox {
>       #mbox-cells = <0>;
>       compatible = "arm,smc-mbox";
>       method = "smc";
>       transports = "mem";
>       arm,func-id = <0xc20000fe>;
>     };
>
>     smc_rx_mbox: rx_mbox {
>       #mbox-cells = <0>;
>       compatible = "arm,smc-mbox";
>       method = "smc";
>       transports = "mem";
>       arm,func-id = <0xc20000ff>;
>     };
>
>     firmware {
>       scmi {
>         compatible = "arm,scmi";
>         mboxes = <&smc_tx_mbox>, <&smc_rx_mbox 1>;
>         mbox-names = "tx", "rx";
>         shmem = <&cpu_scp_lpri>, <&cpu_scp_hpri>;
>       };
>     };
>
Yes, the channel part is good.
But I am not convinced by the need to have SCMI specific "transport" mode.

thanks