Re: [PATCH v4 25/36] nds32: Miscellaneous header files
From: Greentime Hu
Date: Tue Dec 19 2017 - 21:35:32 EST
2017-12-19 17:54 GMT+08:00 Arnd Bergmann <arnd@xxxxxxxx>:
> On Tue, Dec 19, 2017 at 6:34 AM, Greentime Hu <green.hu@xxxxxxxxx> wrote:
>> Hi, Arnd:
>> 2017-12-18 19:13 GMT+08:00 Arnd Bergmann <arnd@xxxxxxxx>:
>>> On Mon, Dec 18, 2017 at 7:46 AM, Greentime Hu <green.hu@xxxxxxxxx> wrote:
>>>> From: Greentime Hu <greentime@xxxxxxxxxxxxx>
>>>> This patch introduces some miscellaneous header files.
>>>> +static inline void __delay(unsigned long loops)
>>>> + __asm__ __volatile__(".align 2\n"
>>>> + "1:\n"
>>>> + "\taddi\t%0, %0, -1\n"
>>>> + "\tbgtz\t%0, 1b\n"
>>>> + :"=r"(loops)
>>>> + :"0"(loops));
>>>> +static inline void __udelay(unsigned long usecs, unsigned long lpj)
>>>> + usecs *= (unsigned long)(((0x8000000000000000ULL / (500000 / HZ)) +
>>>> + 0x80000000ULL) >> 32);
>>>> + usecs = (unsigned long)(((unsigned long long)usecs * lpj) >> 32);
>>>> + __delay(usecs);
>>> Do you have a reliable clocksource that you can read here instead of doing the
>>> loop? It's generally preferred to have an accurate delay if at all possible, the
>>> delay loop calibration is only for those architectures that don't have any
>>> way to observe how much time has passed accurately.
>> We currently only have atcpit100 as clocksource but it is an IP of SoC.
>> These delay API will be unavailable if we changed to another SoC
>> unless all these timer driver provided the same APIs.
>> It may suffer our customers if they forget to port these APIs in their
>> timer drivers when they try to use nds32 in the first beginning.
> Ok, thanks for the clarification.
>> Or maybe I can use a CONFIG_USE_ACCURATE_DELAY to keep these 2
>> implementions for these purposes?
> I'd just add a one-line comment in delay.h to explain that there is no
> cycle counter in the CPU.
Got it. I will add a one-line comment in delay.h