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. > Thanks. Got it. I will add a one-line comment in delay.h -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html