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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Fri, 17 Nov 2017 13:50:02 +0100
Message-ID: <CAK8P3a0ZvAMzG2nRm6Lo8DzdCu-=cCvuWX3ExHtYXP9zOsQ_4Q@mail.gmail.com>
Subject: Re: [PATCH 26/31] nds32: Build infrastructure
To:     Greentime Hu <green.hu@gmail.com>
Cc:     Greentime <greentime@andestech.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jason Cooper <jason@lakedaemon.net>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Rob Herring <robh+dt@kernel.org>,
        Networking <netdev@vger.kernel.org>,
        Vincent Chen <vincentc@andestech.com>
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On Fri, Nov 17, 2017 at 1:39 PM, Greentime Hu <green.hu@gmail.com> wrote:
> 2017-11-10 16:26 GMT+08:00 Greentime Hu <green.hu@gmail.com>:
>> 2017-11-09 18:33 GMT+08:00 Arnd Bergmann <arnd@arndb.de>:
>>> On Thu, Nov 9, 2017 at 10:02 AM, Greentime Hu <green.hu@gmail.com> wrote:
>>>> 2017-11-08 18:16 GMT+08:00 Arnd Bergmann <arnd@arndb.de>:
>>>>> On Wed, Nov 8, 2017 at 6:55 AM, Greentime Hu <green.hu@gmail.com> wrote:
>>>
>>>>>> +config GENERIC_CALIBRATE_DELAY
>>>>>> +       def_bool y
>>>>>
>>>>> It's better to avoid the delay loop completely and skip the calibration,
>>>>> if your hardware allows.
>>>>
>>>> Thanks.
>>>> Do you mean that this config should be def_bool n?
>>>> why? Almost all arch enable it.
>>>
>>> It depends on what your hardware can do. If you have a way to see how much
>>> time has passed that is guaranteed to be reliable on all machines, then
>>> use that instead.
>>>
>>> On a lot of architectures, it's not possible, so they have to fall back to using
>>> the delay loop.
>>
>> I get it. I will discuss it with our HW colleagues.
>> We may get these informations in some registers.
>
> Hi, Arnd:
>
> I think I can't set it to default n because it will be called in start_kernel.
>
> start_kernel() -> calibrate_delay()
>
> If I don't enable this config, it will link error because it didn't
> build init/calibrate.c

You will have to provide an architecture-specific implementation of
this function, please ahve a look at what others are doing, e.g. tile,
openrisc or
h8300.

          Arnd

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