Re: [PATCH 3/5] Deforest the function pointer jungle in the time code.

[Sergei Shtylyov <sshtylyov@ru.mvista.com>]

Maciej W. Rozycki wrote:

>>I don't see how you can have hrtimer support if you choose a periodic
>>timer...

>  Well, periodic timers do seem to work somehow for everybody else with no 
> hassle whatsoever,

    Except the purely periodic timers can't serve as HRT (unless one cheats 
and also declares them as one-shot).

> starting from the DEC code I referred to and including 
> other platforms, like the i386, which uses the 8254 for the timer 
> interrupt and as a HPT, by default, the very same counter or the TSC in 

    What do you mean by HPT -- clocksource?

> the CPU if available or, I think, some chipset timer, because some 

    Weel there was ACPI timer (32-bit free running counter, IIRC) -- but 
somehow I was unable to find the code for it in the current source. And there 
is HPET which is indeed preferred over broken TSC.

> brilliant soul decided to break the TSC at one point.

>  Note that the 8254 can be reprogrammed into a one-shot mode, but somehow 
> nobody does it. ;-)

    Well, hrtimers can do it but the LAPIC timer is preferred over 8254.

>  Similarly for the local APIC timer that is used for 
> scheduling on i386 systems (if available).

    LAPIC timer is also used for HRT, i.e. in one-shot mode (simply because 
it's the best choice for such purpose -- HRTs are per-CPU).

>>>mips_timer_state appropriately, i.e. to flip at the HZ rate (it may be
>>>based on one of the south bridge choices mentioned above or some
>>>free-running counter for example), but people seem to prefer to write
>>>their own code for some reason. ;-)

>>Do you have any examples in mind which rewrite their own calibration
>>code ? I'm too lazy to search into all board code.

>  See arch/mips/mips-boards/generic/time.c for example.  Or any platform 
> that uses the CP0 timer interrupt and has a configurable CPU frequency -- 
> you can find them easily by looking for ones that calculate 
> mips_hpt_frequency rather than set it to a fixed value.

    Alchemy for one.

>   Maciej

WBR, Sergei