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[Blueprint cpuidle-smp-drivers] CPUidle driver changes needed for SMP ARM platforms

 

Blueprint changed by Amit Kucheria:

Whiteboard changed:
  [mturquette 2011/05/06]
  Tegra implements this in an interesting way with some interrupt mechanism to signal between CPUs in the CPUidle driver:
  http://android.git.kernel.org/?p=kernel/tegra.git;a=blob;f=arch/arm/mach-tegra/cpuidle.c;h=a063c34ecf60aa142df1652ecb6b274794fe528e;hb=refs/heads/android-tegra-2.6.36-honeycomb
  
  As an example of driver that needs adapting, the OMAP4 CPUidle driver in the Android tree expects CPU1 to be taken offline via hotplug framework before CPU0 takes the whole ARM cluster down to a lower C-state:
  http://git.omapzoom.org/?p=kernel/omap.git;a=blob;f=arch/arm/mach-omap2/cpuidle44xx.c;h=5e3071d492f21d371afc99130d9133fd1e007ee1;hb=refs/heads/p-android-omap-2.6.35#l78
  
  Main discussion that needs to take place @ UDS is:
  
  1) do we like the approach Tegra takes for other ARM platforms?
  2) is it relevant/possible to other ARM platforms?
  3) what consolidation can take place here?
  4) division of labor to implement platform-specific bits
  
  ---
  
  Discussion from LDS revealed:
  
  1) Other platforms have a similar solution to Tegra and don't *require* Hotplug for CPUidle functionality.
      a) OMAP implementation needs to be updated to remove hotplug dependency
      b) What other platforms need updating?
      c) Should wait on Lorenzo's idle consolidation patches?
  2) Hotplug is still desirable from the power optimization perspective
  
  [1-13-2012] based on note from Mike Turqueete the SMP CPUidle patches
  that were developed for OMAP by the Android folks have been posted to
  the Linux OMAP mailing list.  See,
  http://thread.gmane.org/gmane.linux.ports.tegra/2649/focus=68788
  
  So that action is unblocked now.  What remains is to determine if the
  other platforms can also implement an SMP CPUidle.  Maybe the platform
  owners can be assigned this task?
+ 
+ [amitk, 29/11/2012] SMP cpuidle has progressed a great deal now though
+ included support for coupled C-states from android. This blueprint is
+ superseded by new work.

-- 
CPUidle driver changes needed for SMP ARM platforms
https://blueprints.launchpad.net/linaro-power-kernel/+spec/cpuidle-smp-drivers