Date: Tue, 22 Mar 2011 22:59:32 -0400 (EDT)
From: Len Brown <lenb@kernel.org>
To: Trinabh Gupta <trinabh@linux.vnet.ibm.com>
Cc: arjan@linux.intel.com, peterz@infradead.org, suresh.b.siddha@intel.com,
        benh@kernel.crashing.org, venki@google.com, ak@linux.intel.com,
        linux-kernel@vger.kernel.org, sfr@canb.auug.org.au
Subject: Re: [RFC PATCH V4 2/5] cpuidle: list based cpuidle driver registration
 and selection
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 <20110322123233.28725.92874.stgit@tringupt.in.ibm.com>
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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

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