[RFC PATCH 1/5] arm:omap1/2/3/4:Convert 32k-Sync clocksource driver to platform_driver

[Hiremath, Vaibhav]

On Wed, Jan 18, 2012 at 19:55:51, Marc Zyngier wrote:
> On 18/01/12 14:11, Russell King - ARM Linux wrote:
> > On Wed, Jan 18, 2012 at 01:34:55PM +0000, Hiremath, Vaibhav wrote:
> >> On Wed, Jan 18, 2012 at 17:29:52, Russell King - ARM Linux wrote:
> >>> On Wed, Jan 18, 2012 at 04:58:02PM +0530, Vaibhav Hiremath wrote:
> >>>> Convert counter_32k clocksource driver to standard platform_driver
> >>>> and move it drivers/clocksource/ directory.
> >>>>
> >>>> Also, rename it to more generic name "omap-32k.c".
> >>>
> >>> NAK.  sched_clock is supposed to be available early.  Platform device
> >>> driver initialization is FAR too late.
> >>>
> >> Russell,
> >>
> >> Sched_clock is available very early during boot sequence. Initially gp-timer 
> >> (dmtimer) will get registered as a clocksource. Please refer to the file
> >> mach-omap2/timer.c
> >>
> >> 32k_sync timer (omap-32k.c) will come get registered during arch_init.
> >>
> >> Just FYI, the way I tested it is, I used kernel parameter 
> >> "clocksourse=counter-32k", the switch from gp-timer to 32k timer
> >> will happen once it gets registered.
> > 
> > So please delete the sched_clock code from the 32k timer stuff you've
> > moved to a platform driver.  It will cause sched_clock to reset to zero,
> > and that's bad news.
> > 
> > Only one sched_clock() should ever be registered, and that should only be
> > registered very early at boot time.
> 
> The kernel will WARN if two sched_clock() are registered. I hope this
> will be enough for people not to persist with such a thing...
> 
Marc,

This code-snippet is not registering multiple sched_clock() functions,
Here we have 2 timers
  - gp-timer (available on all devices)
  - 32k-sync timer (may not available on all devices, like AM33xx)

So we are registering both the timers as a clocksource and kernel
Chooses one based on kernel-parameter or rating.
>From sched_clock perspective, we have only one function exported in
mach-omap2/timer.c, which in-turn calls omap-32k.c timer api.

Something like this,


unsigned long long notrace sched_clock(void)
{
	U32 cyc;

	/* First call 32k-sync timer sched_clock() */
	/* return 0 means, the device doesn't have 32k-sync timer available */
	cyc = sched_clock_32k();
	if (cyc)
		return cyc;

	/* Fall back to gp-timer approach */
}

So there is and will not be any warning from kernel here.

Thanks,
Vaibhav
> 	M.
> -- 
> Jazz is not dead. It just smells funny...
> 
>