[Techteam] Weekend 10/31
dsaxena at laptop.org
Mon Nov 3 13:50:28 EST 2008
On Nov 03 2008, at 12:45, Richard A. Smith was caught saying:
> result = cpuidle_register_driver(&acpi_idle_driver);
> looking at this file I see that its called from
> static int __init acpi_processor_init(void)
> This is the same routine that creates a /proc/acpi directory which does
> not exist on the XO so that plus the fact that I know we have ACPI
> disabled I'm assuming that this routine is not called.
> Further greping for 'cpuidle_' I find that the only places cpuidle_
> functions are called is in drivers/acpi/processor_core.c and
> driver/acpi/processor_idle.c .
> If its used in another archs besides x86 can you point me to the code?
> Perhaps I'm not grepping for the right thing?
driver/cpuidle/cpuidle.c:cpuidle_register_device(). This in turn
calls cpuidle_install_idle_handler() which sets the pm_idle
pointer to cpuidle_idle_call(). pm_idle() is called by
cpu_idle_call() calls the governor's select() function which
pokes at various the bits int the cpuidle_device structure and
the current system state to determine the next state and returns an
index into the cpuidle_device's state table. We then index into the
state table, and call the state's enter() function to perform the
actual CPU swtich.
It looks like to make it work with a non-x86 arch, one would have
to hook the pm_idle() call into the the cpu_idle() routine, for example
arch/arm/kernel/process.c:cpu_idle() on ARM. In our case, we would want
to register an olpc_idle_driver and an olpc_idle_device that exports
the known states. Once those are in place, the generic x86 cpu_idle()
call will call into them via the framework.
>  cpuidle is very hard to google for usage info. There is lots of
> unrelated hits that use the term cupidle. Is there a good reference for
> the stuff thats exposed to userspace other than whats in the kernel docs?
I haven't found anything super useful except for reading the code.
linux-pm list is probably the best place to go for more details.
Deepak Saxena - Kernel Developer, One Laptop Per Child
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