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

["Franck Bui-Huu" <vagabon.xyz@gmail.com>]

Hi,

Maciej W. Rozycki wrote:
>  Well, many platforms have some sort of external timer interrupt sources
> (like an 8254 or an DS1287 or even a more sophisticated timer; sometimes
> integrated in the south bridge and collecting dust there), but people tend
> to follow the path of least resistance and use the CP0 timer, even though
> it is is a valuable resource that may be used for some other purposes.  I
Which other purposes ? CP0 hpt gives generally the highest precision for
a given platform, and it seems to be your case too. I don't see which other
better purpose it can deserve other than hrtimer, tick interrupt...

> think the issue has been raised here many times already.  The CP0 timer
> has its problems too as it is one-shot only and needs complicated recovery
> if an interrupt is missed -- see c0_timer_ack().
Well I would say that because it's one-shot, it's a good timer to choose.
I don't see how you can have hrtimer support if you choose a periodic
timer...

And missed interrupts doens't seem a big deal, and the new kernel time
subsystem handle them for us already.

>  Please note that this generic calibration code may be used for
> calibrating the CP0 timer too -- all that you need is defining
Actually the current patchset breaks it since it changes the calibration
code to be used only for the cp0 hpt calibration. I'll change that.

> 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.

> > > 1. No HPT at all.
> > >
> > > 2. HPT in the chipset.
> > >
> > > 3. HPT in CP0.
> > >
> > > depending on the configuration as determined at the run time, with no
> > > predefined frequency in the cases #2 and #3.
> > Good to know.
>  And FYI for DEC CP0 is meant to be the last resort (current code does not
Again IMHO it should be the first choice if possible.

--
              Franck