[PATCH-V4 3/3] ARM: OMAP: Make OMAP clocksource source selection using kernel param

[Hiremath, Vaibhav]

On Thu, Apr 26, 2012 at 10:06:40, Russ Dill wrote:
> On Tue, Apr 24, 2012 at 2:45 AM, Vaibhav Hiremath <hvaibhav at ti.com> wrote:
> > Current OMAP code supports couple of clocksource options based
> > on compilation flag (CONFIG_OMAP_32K_TIMER). The 32KHz sync-timer
> > and a gptimer which can run on 32KHz or system clock (e.g 38.4 MHz).
> > So there can be 3 options -
> >
> > 1. 32KHz sync-timer
> > 2. Sys_clock based (e.g 13/19.2/26/38.4 MHz) gptimer
> > 3. 32KHz based gptimer.
> >
> > The optional gptimer based clocksource was added so that it can
> > give the high precision than sync-timer, so expected usage was 2
> > and not 3.
> > Unfortunately option 2, clocksource doesn't meet the requirement of
> > free-running clock as per clocksource need. It stops in low power states
> > when sys_clock is cut. That makes gptimer based clocksource option
> > useless for OMAP2/3/4 devices with sys_clock as a clock input.
> > Option 3 will still work but it is no better than 32K sync-timer
> > based clocksource.
> >
> > So ideally we can kill the gptimer based clocksource option but there
> > are some OMAP based derivative SoCs like AM33XX which doesn't have
> > 32K sync-timer hardware IP and need to fallback on 32KHz based gptimer
> > clocksource.
> > Considering above, make sync-timer and gptimer clocksource runtime
> > selectable so that both OMAP and AMXXXX continue to use the same code.
> >
> > Also, in order to precisely configure/setup sched_clock for given
> > clocksource, decision has to be made early enough in boot sequence.
> >
> > So, the solution is,
> >
> > Use kernel parameter ("clocksource=") to override
> > default 32k_sync-timer, in addition to this, we also use hwmod database
> > lookup mechanism, through which at run-time we can identify availability
> > of 32k-sync timer on the device, else fall back to gptimer.
> >
> > Signed-off-by: Vaibhav Hiremath <hvaibhav at ti.com>
> > Signed-off-by: Felipe Balbi <balbi at ti.com>
> > Cc: Santosh Shilimkar <santosh.shilimkar at ti.com>
> > Cc: Kevin Hilman <khilman at ti.com>
> > Cc: Benoit Cousson <b-cousson at ti.com>
> > Cc: Tony Lindgren <tony at atomide.com>
> > Cc: Paul Walmsley <paul at pwsan.com>
> > Cc: Tarun Kanti DebBarma <tarun.kanti at ti.com>
> > Cc: Ming Lei <tom.leiming at gmail.com>
> 
> This fails to boot on my Mistral am37x-evm with omap2plus_defconfig
> 

Thanks Russ, for validating it.

But I do not see any relation between your boot process stuck and this patch.
What is the observation without these patches?

Thanks,
Vaibhav