Re: [PATCH v3 0/7] Add common cpuidle code for consolidation.

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On Tue, Jan 24, 2012 at 12:08:08PM -0800, Kevin Hilman wrote:
> Robert Lee <rob.lee@xxxxxxxxxx> writes:

> > Besides just code consolidation, a
> > default "WFI" state is now used with default parameters that different from your
> > original paramenters. The assumption is that if you have a WFI only idle state,
> > the parameters in the new default WFI are more realistic as a true WFI only
> > hardware state incurs minimal latency(<1us) or power penalty to enter and exit.

> > If your platform actually performs other platform specific functionality upon
> > entering WFI and the default parameters do not accurately reflect the 
> > exit_latency and target_residency given in the common default state, please
> > say so.  

> I'm not sure what you mean by "WFI only".  On OMAP, WFI is the entry
> point for all the idle states, with varying latencies.  The latencies
> are then dependent on how the states are programmed for the various
> power domains.  Upon WFI, the hardware then takes over puts the
> powerdomains to their programmed states.   

The default state in the patches is set up with parameters for a state
that literally only does the WFI and has no other hardware actions taken
adding latencies.  I asked for this because the existing drivers for
most of the SoCs out there currently only support that basic idle state
and when doing something more complex (which most of the SoCs actually
can do in hardware) it's still likely to get used during bringup of the
feature.

If there's varying levels of idle state then the SoC specific code would
need to enumerate them and their varying latencies so that the core can
figure out which one to enter.  This isn't a problem, it's a good thing,
but most SoCs haven't got so far as to need it yet.

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