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

Russell King - ARM Linux linux at arm.linux.org.uk
Fri Jun 3 04:55:00 EDT 2011

On Thu, Jun 02, 2011 at 02:38:23PM -0500, Rob Herring wrote:
> On 06/02/2011 11:56 AM, Marc Zyngier wrote:
>> On Thu, 2011-06-02 at 18:31 +0200, Jean-Christophe PLAGNIOL-VILLARD
>> wrote:
>>> On 15:03 Wed 01 Jun     , 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.
>>>> Cc: Paul Mundt<lethal at linux-sh.org>
>>>> Cc: Magnus Damm<magnus.damm at gmail.com>
>>>> Signed-off-by: Marc Zyngier<marc.zyngier at arm.com>
>>> I propose to switch to early platform devce and earlytimer
>>> this will avoid the arm_late_time_init hook
>>> and will make it cross arch
>> I believe this is orthogonal. shmobile (the only ARM user of
>> late_time_init) is already doing some early_platform stuff for its
>> timers.
>> What I'm trying to achieve here is to make sure the timer on CPU0 is
>> actually up, running and registered as a clock_event_device before we
>> hit the delay loop.
>> Or maybe I've misunderstood what you're pointing me to?
> I believe he is referring to this patch which generically enables the  
> shmobile code for ARM:
> http://www.spinics.net/lists/arm-kernel/msg123736.html
> I don't think it has been pulled into mainline yet.

And I really don't like it:
1. It adds an additional layer of complexity.
2. We end up needing more ways to initialize stuff even earlier in the
   kernel boot sequence.
3. Tracking down what gets called when becomes a lot harder.

At one time there used to be a good rule to follow: Keep it Simple, Damnit.
This doesn't follow that.

And so far, no one has explained _why_ shmobile uses this stuff... so
my presumption at the moment is that there's no real good reason.

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