[PATCH] ARM: local timers: Allow boot CPU to have its timer running early

[lethal@linux-sh.org (Paul Mundt)]

On Fri, Jun 03, 2011 at 09:57:35AM +0100, Russell King - ARM Linux wrote:
> On Wed, Jun 01, 2011 at 03:03:26PM +0100, Marc Zyngier wrote:
> > Currently, the boot CPU has its local timer enabled long after
> > the delay loop has been calibrated. This makes it impossible to
> > boot a system that only uses local timers, like the A15.
> > 
> > Use late_time_init hook to initialize the boot CPU local timer.
> > Since shmobile is already using this hook, add an ARM specific
> > arm_late_time_init hook that platforms can use instead.
> 
> Why do we need to initialize the per-cpu timer in late_time_init() ?
> Is there a reason it doesn't work at time_init(), and if not can it
> be fixed to work there?

There are a number of ordering issues. It's necessary to have the clock
framework and everything else initialized before the per-cpu timer can
come up. While we did originally have this at the end of the time_init()
path there were some interactivity issues with regards to lockdep and
having IRQs initialized too early, which was the principle rationale for
deferring it.