Re: [RFC PATCH V4 2/5] cpuidle: list based cpuidle driver registration and selection

the original cpuidle prototype supported multiple driver registration,
but no production use for it could be imagined, and so it was deleted.

Subsequently on x86, we added intel_idle to replace acpi_idle
and a typical kernel will have them both built in.
We still don't allow mutliple registrations, we just arrange
affairs such that the preferred intel_idle probes before 
the backup, acpi_idle.  If intel_idle recognizes the platform,
its probe succeeds, else acpi_idle gets a go.
If there is a problem with intel_idle, or a comparison needs to be made,
a bootparam is available to tell intel_idle not to probe.

This mechanism takes approximately 10 lines of code -- the bootparam
to disable the preferred driver.

What is the benefit of all the code to support the feature of run-time
multiple driver registration and switching?

thanks,
Len Brown, Intel Open Source Technology Center