linux-kernel - Re: [PATCH v6 06/36] nds32: Kernel booting and initialization

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Date:   Mon, 22 Jan 2018 10:53:07 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Greentime Hu <green.hu@...il.com>
Cc:     Greentime <greentime@...estech.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Networking <netdev@...r.kernel.org>,
        Vincent Chen <deanbo422@...il.com>,
        DTML <devicetree@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        David Howells <dhowells@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-serial@...r.kernel.org,
        Geert Uytterhoeven <geert.uytterhoeven@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Mark Rutland <mark.rutland@....com>, Greg KH <greg@...ah.com>,
        Guo Ren <ren_guo@...ky.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        David Miller <davem@...emloft.net>,
        Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Stafford Horne <shorne@...il.com>,
        Vincent Chen <vincentc@...estech.com>
Subject: Re: [PATCH v6 06/36] nds32: Kernel booting and initialization

On Mon, Jan 22, 2018 at 10:49 AM, Greentime Hu <green.hu@...il.com> wrote:
> 2018-01-20 0:41 GMT+08:00 Arnd Bergmann <arnd@...db.de>:

>>> This implementation is referenced from openrisc.
>>> https://lkml.org/lkml/2017/11/17/228
>>
>> It's correct on openrisc, because that has a reliable cycle counter,
>> and that gets used in its delay function:
>>
>> void __delay(unsigned long cycles)
>> {
>>         cycles_t start = get_cycles();
>>         while ((get_cycles() - start) < cycles)
>>                 cpu_relax();
>> }
>>
>> In my review comment that you cited, I assumed that nds32 had similar
>> hardware.
>>
>> However, as you explained earlier, the nds32 architecture does not provide
>> a cycle counter and the clocksource resolution is not high enough to
>> be a good replacement, so you have to use the traditional delay
>> calibration.
>>
>
> Hi, Arnd:
>
> Thank you for your explanation.
> Will it be ok if I code it like this?
>
> config GENERIC_CALIBRATE_DELAY
>        def_bool y

Yes, I think that should be sufficient.

       Arnd