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

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Date:   Tue, 29 Jan 2019 17:28:48 +0900
From:   "Sugaya, Taichi" <sugaya.taichi@...ionext.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Rob Herring <robh+dt@...nel.org>, 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>,
        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 2019/01/22 20:50, Russell King - ARM Linux admin wrote:
> On Tue, Jan 22, 2019 at 08:36:03PM +0900, Sugaya, Taichi wrote:
>> Hi
>>
>> On 2018/12/04 22:32, Rob Herring wrote:
>>> 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.
>>
>> I have a question about the spin-table.
>> The code "smp_spin_table.c" is only in "arch/arm64/kernel" directory so can
>> not be compiled in arm-v7 arch. That means the spin-table can not be used
>> arm-v7 arch..? , or is there the way to compile the code in arm-v7 arch?
> 
> Why do you think you need it?  Do you have no way to control individual
> CPUs?
> 
> We are going through a process in 32-bit eliminating the "spin table"
> stuff from platforms.
> 

Not always necessary to us and considering the history I think it is not 
suitable to use the spin-table.
I try to use another way.