omap clocksource timer selection: dmtimer OR 32K-Sync timer

[Hiremath, Vaibhav]

On Fri, Jan 13, 2012 at 18:19:24, Shilimkar, Santosh wrote:
> On Fri, Jan 13, 2012 at 1:21 PM, Hiremath, Vaibhav <hvaibhav at ti.com> wrote:
> > Hi,
> >
> > In case of AM33xx family of devices, we do not have 32K Sync timer
> > (32K Counter) available; and the current implementation is based on
> > compile-time option, where clock-source is chosen by something like,
> >
> > File - arch/arm/mach-omap2/timer.c
> >
> > #ifdef CONFIG_OMAP_32K_TIMER
> > static void __init omap2_gp_clocksource_init(int unused, const char *dummy)
> > {
> > ...
> > }
> > #else
> > static void __init omap2_gp_clocksource_init(int unused, const char *dummy)
> > {
> > ...
> > }
> > #endif
> >
> >
> > But in order to support multi-omap build, we must
> > make run-time decision to use the timer for kernel clock-source, either of -
> >
> >  - DMTIMER
> >  - 32K Sync Timer
> >
> > The DMTIMER is already migrated to the HWMOD framework, but 32K Timer code
> > has not yet migrated to it. So the question here is,
> >
> > 1) Does it make sense to migrate counter_32k.c to search entry in hwmod
> >   table and if 32k_sync timer is available in hwmod table then use 32K
> >   timer for Kernel clock-source
> >   OR
> >   Fall back to DMTIMER.
> >
> >   OMAP4 hwmod table already has entry,
> >
> >   static struct omap_hwmod omap44xx_counter_32k_hwmod = {
> >         .name           = "counter_32k",
> >   ...
> >   };
> >
> >   We need to have similar entries in all devices where 32K timer is present.
> >
> > 2) OR simply add another cpu_is_am33xx() and then fall back to dmtimer?
> >   Just to prove this, everything works here, I modified the code for this
> >   and tested it on both AM335x EVM and AM37xEVM and it works fine for me.
> >
> >
> > Any comments?? OR Better approach? OR anything which I am missing here?
> >
> You can register both the clock sources together with different
> rating. Based on rating
> timer code will automatically pick the better clock-source of two.
> Ratings is based on the resolution of the timer.
> 
Santosh,

 - Still current compile time implementation must be changed/cleaned, right?
 - The 32k timer doesn't exist at all on AM33xx device, so you can not
   (and should not) Register this timer. 


Thanks,
Vaibhav

> That should remove the CONFIG option depedency.
> 
> Regards
> Santosh
>