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

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Message-ID: <f5917f71-f15b-a92d-649c-e3f5f5f10698@socionext.com>
Date:   Mon, 3 Dec 2018 16:42:56 +0900
From:   "Sugaya, Taichi" <sugaya.taichi@...ionext.com>
To:     Stephen Boyd <sboyd@...nel.org>, 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

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?

Thanks
Sugaya Taichi

>