Re: [PATCH 3/5] arm64: dts: msm8916: Add spc compat tag

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Fri, Jun 10, 2016 at 12:27:16PM -0500, Andy Gross wrote:
> On Fri, Jun 10, 2016 at 06:06:56PM +0100, Lorenzo Pieralisi wrote:
> > On Fri, Jun 10, 2016 at 11:52:48AM -0500, Andy Gross wrote:
> > 
> > [...]
> > 
> > > > (1) enter_freeze() hooks are not strictly necessary to enable
> > > >     suspend-to-idle (they are if we want the tick to be frozen
> > > >     on suspend-to-idle, which is different)
> > > 
> > > I'd think that you'd want the tick frozen.  Even if you are going to
> > > just call the deepest freezable idle state in your freeze_function,
> > > you don't want to keep getting woken up as this costs some power usage
> > 
> > As I said, that's a separate issue from these bindings.
> 
> I kind of see that coupled with the determination that a idle state
> supports freeze.  Or are you wanting to have something else that
> decides whether or not to configure the enter_freeze?

All PSCI based idle state support freeze, as long as most of the
other idle routines for ARM 32-bit, I do not even think we should
bother with defining DT bindings for it.

[...]

> > For 64-bit you do not have to have add any facility.
> > 
> > 1) we should change core code to make PM_SUSPEND_FREEZE independent
> >    of suspend_set_ops()
> 
> So then, if cpuidle is active and you have idle states supporting
> freeze, then you can always implicitly freeze the system.  This would
> infer then that the system will always indicate it can do freeze.  I
> am good with that.
> 
> For now, we can get away with just implementing the changes you are
> suggesting.

Cracking.

> > 2) we should define which idle states are freezable (99% of them are
> >    minus coupled idle states), through generic bindings
> 
> This would be in the form of a DT property?  And given this property
> then we'd just assign a enter_freeze() function that calls the enter()
> for that state.  Or would we have something else that we need to key
> off of to decide to configure the enter_freeze?

See above, I will give it more thought. I take an action to change
core code as per discussion above.

Thanks for raising the point.

Lorenzo