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

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Message-ID: <90b00858-6e9e-8f7c-f6d4-b35e5daa6eee@socionext.com>
Date:   Tue, 4 Dec 2018 20:30:53 +0900
From:   "Sugaya, Taichi" <sugaya.taichi@...ionext.com>
To:     Rob Herring <robh+dt@...nel.org>
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

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

Thanks
Sugaya Taichi


> 
> Rob
>