[PATCH] OMAP: powerdomains: Make all powerdomain target states as ON at init

[Felipe Balbi]

Hi,

On Fri, Jul 15, 2011 at 02:10:46AM -0600, Paul Walmsley wrote:
> > > diff --git a/arch/arm/mach-omap2/powerdomain.c b/arch/arm/mach-omap2/powerdomain.c
> > > index e0490bc..e61866c 100644
> > > --- a/arch/arm/mach-omap2/powerdomain.c
> > > +++ b/arch/arm/mach-omap2/powerdomain.c
> > > @@ -109,6 +109,16 @@ static int _pwrdm_register(struct powerdomain *pwrdm)
> > >  
> > >  	list_add(&pwrdm->node, &pwrdm_list);
> > >  
> > > +	/*
> > > +	* Program all powerdomain target state as ON; This is to
> > > +	* prevent domains from hitting low power states (if bootloader
> > > +	* has target states set to something other than ON) and potentially
> > > +	* even losing context while PM is not fully initilized.
> > > +	* The PM late init code can then program the desired target
> > > +	* state for all the power domains.
> > > +	*/
> > > +	pwrdm_set_next_pwrst(pwrdm, PWRDM_POWER_ON);
> > 
> > Just out of curiosity, I was wondering if it really makes sense to power
> > up all power domains during boot just to avoid loosing context. Doesn't
> > hwmod/omap_device soft-reset all IPs during initialization ? If that's
> > really the case, shouldn't we then choose which powerdomains are
> > strictly necessary for boot and only power those up ?
> > 
> > Sorry if this is a non-sensical question, but I was curious about it
> > ;-)
> 
> This patch only sets the powerdomain's next power state to ON.  It doesn't 
> affect the current power state of the powerdomain.
> 
> Let's say that the bootloader, previous OS (in the kexec case), or ROM 
> code programs the next power state of some powerdomains to OFF.  Let's 
> also say that the kernel that is booted has PM disabled.  The moment a 
> powerdomain's clockdomains go inactive, the powerdomain will then switch 
> off and all devices in that powerdomain will lose context.  On a 
> non-PM-enabled kernel, that will be unexpected and will probably cause the 
> system to crash.  This patch prevents that from happening.

I see... thanks for clarifying. The comment above the code wasn't really
clear about it to me.

-- 
balbi
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