linux-kernel - Re: [PATCH 02/14] dt-bindings: soc: milbeaut: Add Milbeaut trampoline description

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Message-ID: <154356579701.88331.5043467509900444879@swboyd.mtv.corp.google.com>
Date:   Fri, 30 Nov 2018 00:16:37 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     "Sugaya, Taichi" <sugaya.taichi@...ionext.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-serial@...r.kernel.org
Cc:     Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Russell King <linux@...linux.org.uk>,
        Jiri Slaby <jslaby@...e.com>,
        Masami Hiramatsu <masami.hiramatsu@...aro.org>,
        Jassi Brar <jaswinder.singh@...aro.org>
Subject: Re: [PATCH 02/14] dt-bindings: soc: milbeaut: Add Milbeaut trampoline
 description

Quoting Sugaya, Taichi (2018-11-29 04:24:51)
> On 2018/11/28 11:01, Stephen Boyd wrote:
> > Quoting Sugaya Taichi (2018-11-18 17:01:07)
> >>   create mode 100644 Documentation/devicetree/bindings/soc/socionext/socionext,m10v.txt
> >>
> >> diff --git a/Documentation/devicetree/bindings/soc/socionext/socionext,m10v.txt b/Documentation/devicetree/bindings/soc/socionext/socionext,m10v.txt
> >> new file mode 100644
> >> index 0000000..f5d906c
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/soc/socionext/socionext,m10v.txt
> >> @@ -0,0 +1,12 @@
> >> +Socionext M10V SMP trampoline driver binding
> >> +
> >> +This is a driver to wait for sub-cores while boot process.
> >> +
> >> +- compatible: should be "socionext,smp-trampoline"
> >> +- reg: should be <0x4C000100 0x100>
> >> +
> >> +EXAMPLE
> >> +       trampoline: trampoline@...C000100 {
> > Drop the 0x part of unit addresses.
> 
> Okay.
> 
> 
> >> +               compatible = "socionext,smp-trampoline";
> >> +               reg = <0x4C000100 0x100>;
> > Looks like a software construct, which we wouldn't want to put into DT
> > this way. DT doesn't describe drivers.
> We would like to use this node only getting the address of the 
> trampoline area
> in which sub-cores wait.  (They have finished to go to this area in previous
> bootloader process.)

Is this area part of memory, or a special SRAM? If it's part of memory,
I would expect this node to be under the reserved-memory node and
pointed to by some other node that uses this region. Could even be the
CPU nodes.

> 
> So should we embed the constant value in source codes instead of getting 
> from
> DT because the address is constant at the moment? Or is there other 
> approach?
> 

If it's constant then that also works. Why does it need to come from DT
at all then?