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

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Message-ID: <CAL_JsqJ=FRfzVFiOJ0wvoV5iZV+Gx3ft9pGyhb-GoKnOAQgPtQ@mail.gmail.com>
Date:   Tue, 4 Dec 2018 07:32:41 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     sugaya.taichi@...ionext.com
Cc:     Stephen Boyd <sboyd@...nel.org>, devicetree@...r.kernel.org,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Michael Turquette <mturquette@...libre.com>,
        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

On Tue, Dec 4, 2018 at 5:30 AM Sugaya, Taichi
<sugaya.taichi@...ionext.com> wrote:
>
> Hi
>
> On 2018/12/04 0:49, Rob Herring wrote:
> > On Mon, Dec 3, 2018 at 1:42 AM Sugaya, Taichi
> > <sugaya.taichi@...ionext.com> wrote:
> >>
> >> Hi,
> >>
> >> On 2018/11/30 17:16, Stephen Boyd wrote:
> >>> 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.
> >>
> >> Yes, 0x4C000100 is a part of memory under the reserved-memory node. So
> >> we would like to use the SRAM ( allocated 0x00000000 ) area instead.
> >> BTW, sorry, the trampoline address of this example is simply wrong.  We
> >> were going to use a part of the SRAM from the beginning.
> >>
> >>>
> >>>>
> >>>> 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?
> >>
> >> We think it is not good to embed constant value in driver codes and do
> >> not have another way...
> >> Are there better ways?
> >
> > If this is just memory, can you use the standard spin-table binding in
> > the DT spec? There are some requirements like 64-bit values even on
> > 32-bit machines (though this gets violated).
>
> The spin-table seems to be used on only 64-bit arch. Have it ever worked
> on 32-bit machine?

Yes.

> And I would like not to use it because avoid violation.

The issue now that I remember is cpu-release-addr is defined to always
be a 64-bit value while some platforms made it a 32-bit value.
'cpu-release-addr' is also used for some other enable-methods.

Rob