[PATCH 1/3] ARM: OMAP2+: 32k-counter: Use hwmod lookup to check presence of 32k timer

[Hiremath, Vaibhav]

On Mon, Mar 19, 2012 at 17:14:30, Ming Lei wrote:
> On Mon, Mar 19, 2012 at 7:11 PM, Hiremath, Vaibhav <hvaibhav at ti.com> wrote:
> >
> > I think you made very good point here. With the above patch, we are almost missing the capability of registering dmtimer as a clocksource for OMAP.
> > It will always use 32k-counter, and never fall back to dmtimer.
> >
> > Then the only options we have here is,
> >
> > 1) Register both the timers, 32k-counter and dmtimer for clocksource; let
> >   Kernel pick up best rating clocksource out of these two.
> >
> >   In case of OMAP1/2/3/4, kernel will use dmtimer, since it has better
> >   Rating. User can choose the 32k-counter clocksource via bootargs.
> >
> >   Impact: without bootargs for clocksource selection, kernel will choose
> >     dmtimer, impacting loss of time during suspend/resume.
> >
> >
> > 2) Let the current code be as is, means, the clocksource registration will
> >   Happened based on "#ifdef CONFIG_OMAP_32K_TIMER" and this option
> >   selection will be Controlled by Kconfig rules.
> 
> How about the 3rd option?
> 
> 3), take the way in your patch 1) at default, but will switch to
> register dmtimer
> directly and bypass 32k-counter if user need it via kernel parameter.
> 
> As far as I can think of, the situations required for dmtimer are high-frequency
> perf sample and high precision trace points, so looks it is OK to take
> 32k-counter
> at default.
> 
But if you register both the timers (dmtimer & 32ksync), then initially kernel will only pick up dmtimer, as this has better rating. And late in
the boot sequence clocksource switch will happen, base on 
kernel parameter (clocksource=).

So logically dmtimer will be always used as a default here.

Thanks,
Vaibhav

> Thanks,
> -- 
> Ming Lei
>