surprisingly early suspend

[Benjamin M. Schwartz]

John Watlington wrote:
> I'm under the impression that our desire to stay with a stock operating
> system is one of the big remaining limitations, but could be wrong.

My impression:
Linux is capable of the desired behavior in general, via the cpuidle
framework, which chooses to transition between sleep states based on the
transition latencies, system activity, and upcoming timer events.  Cpuidle
separates policy from implementation by using pluggable backends in the
form of cpuidle drivers that handle state transitions [1].  At present,
the only cpuidle driver in the kernel is the ACPI driver
(drivers/acpi/processor_idle.c).

I do not know whether the XO's CPU deactivation, DCON, and timed wakeup
system can be, or has been, mapped into an ACPI state.  If ACPI is
insufficient to represent the XO's behavior, then a new cpuidle driver
will be required.  I expect such a driver would be accepted into the
upstream kernel.  Writing it should not be hugely difficult, but I do not
have enough experience to provide a good estimate of the amount of work
required.

--Ben

[1] http://www.mjmwired.net/kernel/Documentation/cpuidle/driver.txt



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