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SubjectRe: Fwd: Commit 76a2a6ee8a0660a29127f05989ac59ae1ce865fa breaks PXA270 (at least)?
On Tue, Jul 29, 2008 at 03:46:05PM -0700, Andrew Morton wrote:
> On Tue, 29 Jul 2008 23:31:05 +0100
> Russell King - ARM Linux <linux@arm.linux.org.uk> wrote:
>
> > But then some bright spark thought it would be a good idea to get
> > rid of printk_clock().
>
> <does git-log, searches for printk_clock>
>
> commit 86faf39d0fc04272b05fab1db6d683f3ac7199d1
> Author: Ingo Molnar <mingo@elte.hu>
> Date: Fri Jan 25 21:07:59 2008 +0100
>
> sched: remove printk_clock references from ia64
>
> remove remaining printk_clock references from ia64.
>
> Signed-off-by: Ingo Molnar <mingo@elte.hu>
>
> commit b842271fbb9c8b5fd0e1c3e1895a3b67ba5bcc54
> Author: Ingo Molnar <mingo@elte.hu>
> Date: Fri Jan 25 21:07:59 2008 +0100
>
> sched: remove printk_clock()
>
> printk_clock() is obsolete - it has been replaced with cpu_clock().
>
> Signed-off-by: Ingo Molnar <mingo@elte.hu>
>
>
> That's it? It rates a 0.5/10 for changelogging :(
>
> Looking further on...
>
> commit e97126cd9056b3b42cdc862ace2ed66f8026f55b
> Author: Russell King <rmk@dyn-67.arm.linux.org.uk>
> Date: Mon Jan 8 19:49:12 2007 +0000
>
> [ARM] Provide basic printk_clock() implementation
>
> Current sched_clock() implementations on ARM cause unbootable kernels
> with PRINTK_TIME support enabled. To avoid this, provide a basic
> printk_clock() implementation which avoids sched_clock() being called
> before the page tables have been set up.
>
>
> which I assume is why arm is crashing again?

Precisely - Ingo has effectively progressively backed out my bug fix
in a round-about manner by making printk require a working sched_clock
again.

> Really, I think arch-overrideable printk_clock() was a good idea.
> printk is just _special_. It's called wildly early and it is called in
> all conceivable contexts and it just must work no matter what. It's
> totally understandable that an architecture would need to override
> printk's timestamp generator.

That's one solution, the other is to have that commit reverted. I
don't really mind which, only that we have a solution ASAP so that
the current popular ARM SoCs have a bootable kernel again.


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